chore: bump signet-sdk to 0.18.0 (for real this time)

[Evalir]

Description

Re-bumps the signet stack to actually consume 0.18.0. The previous PR (#274) merged with a title claiming 0.18.0 but its content only moved signet-* to 0.17.0 and left signet-block-processor / signet-genesis on the node-components git tag v0.16.0-rc.10. This catches the builder up and removes the cross-repo git pin.

Version bumps

• init4-bin-base 0.20.0 → 0.21.0
• signet-{constants,sim,tx-cache,types,zenith} 0.17.0 → 0.18.0
• signet-bundle (dev-dep) 0.17.0 → 0.18.0

Dep source changes

• signet-block-processor and signet-genesis move from node-components@v0.16.0-rc.10 (git) → crates.io 0.18.0 now that they're published there.
• signet-block-processor is removed — it was only there for revm_spec, which was deleted upstream in node-components v0.17.0 when the reth dep was dropped.
• signet-evm = "0.18.0" added — that's where the replacement helper lives.

Source migration in SignetCfgEnv

• revm_spec(chainspec, timestamp) → EthereumHardfork::active_hardforks(&chainspec.genesis().config, block_number, timestamp).spec_id().
• SignetCfgEnv now carries block_number next to timestamp (the new helper needs both for full fork resolution). Threaded through 5 call sites.
• Added SignetCfgEnv::from_block_env(chain_id, &BlockEnv) so the 4 BlockEnv-derived sites stay one-liners. prep.rs keeps new() since it builds for the next block from a Header.

Behavior note

Old revm_spec had a hard PRAGUE floor; the new path reports whatever the genesis config says is active. Cross-checked against the actual signet-genesis configs:

• Rollup configs (mainnet, parmigiana) activate every fork at timestamp 0 → both old and new return OSAKA for any timestamp ≥ 0.
• Host config (real Ethereum mainnet schedule, prague=May 2025 / osaka=Dec 2025) → all current production timestamps are past Osaka, so both paths return OSAKA.
• The floor would only have mattered for pre-Prague host timestamps, which nothing in the builder reaches today.

Related Issue

Closes ENG-2235 (carried over from #274).

Testing

• cargo clippy --workspace --all-targets --all-features -- -D warnings
• cargo test -p builder --lib tasks::block::cfg (the mainnet_cfg_env PRAGUE↔OSAKA spec-resolution test passes)
• make fmt
• make clippy
• make test

[Evalir]

• chore: bump signet-sdk to 0.18.0 (for real this time) #276 👈 (View in Graphite)
• main

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