clients: wire HIVE_TARGET_GAS_LIMIT for besu, erigon, reth, ethrex

[MysticRyuujin]

Summary

Pass HIVE_TARGET_GAS_LIMIT to the client's target gas limit flag in the besu, erigon, reth, and ethrex wrappers. Only go-ethereum and nethermind consumed it before.

client	flag
besu	--target-gas-limit
erigon	--miner.gaslimit
reth	--builder.gaslimit
ethrex	--builder.gas-limit

Why

#1585 defaults HIVE_TARGET_GAS_LIMIT to 60,000,000 in rpc-compat so that testing_buildBlockV1 builds deterministic blocks across clients. A client that does not consume the variable keeps its own default and builds a different gas limit, which changes the block hash. Besu fails 2 of 4 buildBlockV1 tests on current execution-apis fixtures for this reason.

Verification

Ran rpc-compat/testing_buildBlockV1 with besu (main), erigon and reth (glamsterdam-devnet-8 images) before and after, on both the current fixtures and the ethereum/execution-apis#867 Amsterdam fixtures:

• besu: 2 failed → 0 failed on both fixture sets.
• erigon, reth: unchanged, no regression. Erigon's remaining Amsterdam failures are unrelated to this variable: it requires targetGasLimit in the payload attributes for Glamsterdam+ (fix: add slotNumber and targetGasLimit to testing_buildBlockV1 execution-apis#862), which node configuration cannot supply.
• ethrex: flag verified against the image's --help; not exercised at runtime because ethrex cannot import the rpc-compat chain (Exit the client if on a pre merge fork lambdaclass/ethrex#5504).

An alternative is to emit the value from hivechain's forkenv output. The sim-side default from #1585 already covers where the value comes from, so this PR only adds the client-side consumption.

[danceratopz]

Hey @MysticRyuujin, this LGTM.

Sorry for the commit noise here, I saw that nimbus-el wasn't added, before realizing that this flag was marked as deprecated and that nimbus doesn't support testing_buildBlockV1, so reverted that commit!