ethrex integration: Crypto-trait guest + synthetic block fixture generator

[ColoCarletti]

Description

⚠️ Temporary. This pins our ethrex guest to the unmerged LambdaVM-backend ethrex PR branch and adds an in-repo fixture generator as a stand-in. Once that PR merges to ethrex main, we re-pin to the merge commit and switch fixture generation to ethrex-replay. The in-repo generator is then removed.

What this does

• Migrates the ethrex guest to the new Crypto-trait API (execution_program(input, LambdaVmCrypto)); keccak runs through our precompile. Removes the old [patch] ethrex-crypto and c-kzg.
• Adds tooling/ethrex-fixtures — a small offline tool that builds ethrex blocks with an arbitrary number of ETH transfers and writes the serialized
  ProgramInput. Pinned to the same ethrex rev as the guest so fixtures stay compatible.
• Regenerates the committed fixtures (empty / 1-tx / 10-tx) at the new rev and wires empty + 1-tx into the ethrex benchmark.
• Updates the executor's native test reference + docs.

[github-actions]

Codex Code Review

No issues found in the PR diff.

Notes:

• I reviewed only 55e8c7b1...fe199d41.
• git diff --check passed.
• Fixture SHA-256 values in executor/tests/README.md match the checked-in binaries.
• I could not run cargo check: Cargo tried to write git dependencies under read-only /home/runner/.cargo/git.

[github-actions]

Benchmark Results for unmodified programs 🚀

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
base binary_search	49.9 ± 1.3	48.5	52.2	1.00
head binary_search	50.2 ± 1.1	48.5	51.8	1.01 ± 0.03

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
base bitwise_ops	50.1 ± 1.1	48.6	51.6	1.00
head bitwise_ops	52.7 ± 4.6	48.7	63.6	1.05 ± 0.09

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
base fibonacci_26	54.6 ± 0.6	53.5	55.3	1.00
head fibonacci_26	55.0 ± 1.0	53.7	56.6	1.01 ± 0.02

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
base hashmap	105.4 ± 1.5	103.6	107.6	1.00 ± 0.02
head hashmap	105.2 ± 2.1	103.1	109.4	1.00

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
base keccak	109.2 ± 2.3	106.6	112.5	1.01 ± 0.03
head keccak	108.6 ± 2.2	103.9	110.7	1.00

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
base matrix_multiply	60.7 ± 1.4	59.0	63.0	1.01 ± 0.03
head matrix_multiply	60.0 ± 1.1	58.4	61.6	1.00

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
base modular_exp	50.7 ± 1.0	49.5	52.2	1.01 ± 0.03
head modular_exp	50.3 ± 1.0	49.1	52.0	1.00

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
base quicksort	53.9 ± 0.7	52.6	54.8	1.00
head quicksort	54.2 ± 1.0	52.6	55.7	1.00 ± 0.02

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
base sieve	57.2 ± 1.5	55.1	59.5	1.00 ± 0.04
head sieve	57.0 ± 1.7	54.9	59.9	1.00

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
base sum_array	67.5 ± 1.1	66.2	70.0	1.00
head sum_array	68.6 ± 1.7	66.7	71.4	1.02 ± 0.03

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
base syscall_commit	77.1 ± 1.3	75.5	79.0	1.00
head syscall_commit	78.5 ± 2.8	75.6	85.8	1.02 ± 0.04