feat(core-backend): Add the ability to change backend context

[Lazark0x]

Resolves #4449

Sequential Execution Optimization for Ethexe Runtime

Summary

This PR implements sequential execution optimization for the ethexe runtime, enabling WASM environment reuse across consecutive dispatch executions. By caching execution contexts and avoiding redundant lazy pages setup/teardown between dispatches, we achieve significant gas savings.

Problem

Previously, each dispatch execution in ethexe required:

1. Full lazy pages initialization with memory protection setup
2. Complete WASM environment instantiation
3. Tear down of lazy pages protection after execution
4. Repeat for every single dispatch

This approach incurs substantial overhead when processing multiple dispatches in sequence, as each dispatch paid the full initialization cost (~700M gas) regardless of whether the previous execution could be reused.

Solution

The optimization introduces:

1. PrechargeContext: Caches code, metadata, and environment state between executions
2. Sequential execution mode: Reuses WASM environment when processing multiple dispatches for the same program
3. Deferred lazy pages cleanup: Only performs lazy pages protection setup/teardown once per batch instead of per-dispatch
4. Memory snapshots: Captures memory state for rollback on execution failure

Benchmark Results

Benchmarks comparing gas consumption between this branch and master when processing multiple dispatches (using demo-fungible-token workload with init + mint operations):

Gas Consumption Comparison

Dispatches	Master (Avg Gas)	This Branch (Avg Gas)	Gas Savings
1	361,256,312	361,256,312	0%
2	1,078,332,174	719,961,176	33.2%
3	1,795,408,036	938,808,118	47.7%
5	3,229,559,760	1,376,502,002	57.4%
10	6,814,939,070	2,470,736,712	63.7%
20	13,985,697,690	4,659,206,132	66.7%
50	35,497,973,550	11,224,614,392	68.4%
100	71,351,766,650	22,166,961,492	68.9%

Gas per Dispatch Analysis

Dispatches	Master (Gas/Dispatch)	This Branch (Gas/Dispatch)	Reduction
1	361M	361M	0%
2	539M	360M	33%
5	646M	275M	57%
10	681M	247M	64%
20	699M	233M	67%
50	710M	224M	68%
100	714M	222M	69%

Execution Time Comparison

Dispatches	Master (Time)	This Branch (Time)	Time Savings
1	264µs	257µs	3%
2	414µs	249µs	40%
5	1.04ms	394µs	62%
10	2.13ms	615µs	71%
20	4.20ms	1.06ms	75%
50	10.6ms	2.41ms	77%
100	21.0ms	4.61ms	78%

Key Observations

1. Single dispatch: Identical performance (no optimization opportunity)
2. 2-100 dispatches: 33-69% gas savings, with benefits increasing as dispatch count grows
3. Gas per dispatch: Converges to ~220M (vs ~710M on master) - a 69% reduction in marginal cost
4. Execution time: 40-78% faster, with time per dispatch dropping from ~210µs to ~46µs

Why This Matters

Master's gas consumption scales linearly at ~700M gas per dispatch (full init + execution each time).

This branch's gas consumption is sub-linear:

• First dispatch: ~361M (full init)
• Subsequent dispatches: ~220M (execution only, environment reused)

At 100 dispatches, this means:

• Master: 71.4B gas
• This branch: 22.2B gas
• Savings: 49.2B gas (69%)

[Copilot]

Pull Request Overview

This PR adds functionality to change the backend context by updating environment state handling, memory reset logic and benchmark configurations. Key changes include:

• Modifying various Environment::new calls to use a callback function instead of a DispatchKind parameter.
• Introducing a new memory dump structure and related memory dump/set functions in the core and processor modules.
• Refining benchmarks, gas counter traits and context types to support new backend context capabilities.

Reviewed Changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
utils/wasm-gen/src/tests.rs	Updated test setup using the new Environment::new API
pallets/gear/src/benchmarking/mod.rs	Replaced DispatchKind with callback-based environment creation
core/src/memory.rs	Added PageDump structure and enhanced MemoryError with Default
core/src/gas.rs	Added Eq and PartialEq to GasAmount for improved comparisons
core/src/code/mod.rs	Introduced the new accessor for stack_end
core/src/buffer.rs	Added try_replace method along with a new test case
core-processor/src/lib.rs	Added a testing module for processor extensions
core-processor/src/ext.rs	Implemented new dump_memory and set_memory functions and updated derives
core-processor/src/executor.rs	Updated environment creation and error handling in execute calls
core-processor/src/context.rs	Adjusted SystemReservationContext with Eq and PartialEq derives
core-processor/Cargo.toml	Updated dependencies/features with optional modules for lazy-pages
core-backend/src/lib.rs	Revised Environment::new usage and execute call to support backend context changes