Replace command building with direct socket method calls

[bisho]

Refactor DefaultExecutor to use MemcacheSocket meta_* methods directly

This PR refactors the DefaultExecutor class to use the new blocking meta_* methods from MemcacheSocket instead of manually building commands and handling send/receive operations separately.

Changes Made

• Replaced command building with direct method calls: Removed _build_cmd() method and updated exec_on_pool() to use _conn_exec_cmd() which calls conn.meta_get(), conn.meta_set(), etc. directly
• Consolidated response processing: Extracted common response processing logic into _process_response() method to handle deserialization and error handling consistently
• Updated pipelining methods: Modified _conn_send_cmd() to use conn.send_meta_*() methods and simplified _conn_recv_response() to reuse the common response processing logic
• Enhanced test coverage: Added comprehensive wire-format tests using a new WireSocket fixture that captures actual bytes sent over the socket, replacing mock-based assertions with real wire protocol verification

Benefits

• Cleaner separation of concerns: The executor now focuses on high-level operations while delegating protocol details to the socket layer
• Reduced code duplication: Common response processing logic is centralized
• Better test coverage: Wire-format tests ensure protocol correctness and catch regressions in the actual bytes sent
• Improved maintainability: Less manual command construction and response parsing

The changes maintain full backward compatibility while making the codebase more robust and easier to maintain.

Performance

Common config: server 127.0.0.1:11211, 10 threads, 1.00M requests (4 runs × 25,000 ops × 10 threads), 200 key space, GC disabled, 160/200 keys populated (95% small 80-250B, 5% large 100KB)                                                                                
                                                                                                                                                                                                                                                                              
  ┌───────────────┬────────┬─────────┬──────────────────────┬──────────────────────┐                                                                                                                                                                                                              
  │               │        │         │    Socket in Rust    │    meta_* in Rust    │
  │   Operation   │        │ BEFORE  ├──────────┬───────────┼──────────┬───────────┤                                                                                                                                                                                                              
  │               │        │         │  Result  │  Speedup  │  Result  │  Speedup  │                                                                                                                                                                                                              
  ├───────────────┼────────┼─────────┼──────────┼───────────┼──────────┼───────────┤                                                                                                                                                                                                              
  │               │ RPS    │  46,600 │   76,652 │           │  110,287 │           │                                                                                                                                                                                                              
  │  SET          ├────────┼─────────┼──────────┤   1.65x   ├──────────┤   2.37x   │                                                                                                                                                                                                              
  │               │ us/req │   21.46 │    13.05 │           │     9.07 │           │                                                                                                                                                                                                              
  ├───────────────┼────────┼─────────┼──────────┼───────────┼──────────┼───────────┤                                                                                                                                                                                                              
  │               │ RPS    │  46,135 │   81,401 │           │  116,382 │           │                                                                                                                                                                                                              
  │  GET          ├────────┼─────────┼──────────┤   1.76x   ├──────────┤   2.52x   │                                                                                                                                                                                                              
  │               │ us/req │   21.68 │    12.28 │           │     8.59 │           │                                                                                                                                                                                                              
  ├───────────────┼────────┼─────────┼──────────┼───────────┼──────────┼───────────┤                                                                                                                                                                                                              
  │               │ RPS    │   2,677 │    3,626 │           │    3,560 │           │                                                                                                                                                                                                              
  │  MULTI_GET(5) ├────────┼─────────┼──────────┤   1.35x   ├──────────┤   1.33x   │                                                                                                                                                                                                              
  │               │ us/req │  373.52 │   275.81 │           │   280.86 │           │                                                                                                                                                                                                              
  ├───────────────┼────────┼─────────┼──────────┼───────────┼──────────┼───────────┤                                                                                                                                                                                                              
  │               │ RPS    │  48,080 │   82,886 │           │  123,053 │           │                                                                                                                                                                                                              
  │  DELETE       ├────────┼─────────┼──────────┤   1.72x   ├──────────┤   2.56x   │                                                                                                                                                                                                              
  │               │ us/req │   20.80 │    12.06 │           │     8.13 │           │                                                                                                                                                                                                              
  └───────────────┴────────┴─────────┴──────────┴───────────┴──────────┴───────────┘

[bisho]

• Add batch multi-get execution for improved performance #83
• Make key encoder optional and remove default implementation #82
• Replace command building with direct socket method calls #81 👈 (View in Graphite)
• Migrate MemcacheSocket implementation to Rust #80
• Enhance benchmark with comprehensive SET/GET/DELETE testing #79
• main

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[xmartinez]

LG! (Just one nit)

[bisho]

Merge activity

• Mar 26, 3:31 PM UTC: A user started a stack merge that includes this pull request via Graphite.
• Mar 26, 3:36 PM UTC: Graphite rebased this pull request as part of a merge.
• Mar 26, 3:37 PM UTC: @bisho merged this pull request with Graphite.