feat(blocklog): parse ethrex block execution throughput logs

[edg-l]

What

Implements the ethrex block-log parser in pkg/blocklog (replacing the stub), so ethrex runs produce per-block metrics like the other clients.

It parses ethrex's per-block execution metric header (emitted on the engine_newPayload path) into the shared { "block": { "hash": ... }, ... } shape:

[METRIC] BLOCK 24358000 0x<hash> | 1.234 Ggas/s | 567.00 ms | 150 txs | 700 Mgas (93%)

Captured fields: block.number, block.hash, block.gas_used_mgas, block.gas_used_pct, block.tx_count, throughput.ggas_per_sec, timing.total_ms. ANSI is stripped; the hash is optional in the regex so the line still parses on builds that don't log it (it just won't match a test without block.hash).

Dependency

Matching a log to a test requires block.hash, and ethrex does not yet include the hash on this line. That is addressed upstream in lambdaclass/ethrex#6736, which adds the hash exactly where this parser expects it (BLOCK <num> 0x<hash> | ...). Once that lands and reaches the ethrex image used here, ethrex runs will start attaching per-block metrics.

Marking this draft until the ethrex change is merged and released.

Notes

• ethrex follows this header with separate |- validate/exec/merkle/store lines; since the collector matches one payload per line by hash, only the header is captured. Folding in the phase breakdown would need ethrex to emit a single structured line (follow-up).
• Test coverage mirrors reth_test.go: hash / no-hash / zero-gas / ANSI / non-matching lines. gofmt, go vet, and go test ./pkg/blocklog/ pass.