feat(node): validator cert

[cryptoAtwill]

This PR improves the previous PR by introducing a bitmap to count which validator has pre-commit vote signature included.

This excludes:

• Validator with no submission
• Validator with nil vote

Then contract will validate the cert onchain.

The point of this PR is to reduce gas usage for cometbft light client verification.

---

Note

Introduce bitmap-backed validator certificates for CometBFT quorum, adjust checkpoint/app-hash handling, and wire through node, CLI, and provider with new APIs and validations.

• Contracts (Solidity):
  • Light client: Replace signature array with ValidatorCertificate { bitmap, signatures }; quorum verification iterates via bitmap.
  • Checkpointing: submitBottomUpCheckpoint now accepts (LightHeader, ValidatorCertificate, CanonicalVote) and treats app hash as height-1; add lastCommitmentHeight, rename internal tracking; recordAppHashBreakdown enforces sequencing and only records non-empty batches; expose deriveAppHash/validateAppHash as public.
  • Validation: Enforce activeValidatorsLimit <= uint8::MAX; add TooManyValidators; change InvalidCheckpointEpoch to include (expected, actual).
  • Selectors/Tests: Update selectors and integration tests; add new SubnetCheckpoint tests.
• Provider/Relayer (Rust):
  • Add ValidatorCertificate ABI type and bitmap construction; submit_signed_header now sends certificate; new get_last_app_commitment_height and app-hash breakdown submission uses Fendermint state root.
  • CLI relayer requires --fendermint-rpc-url; integrate fendermint_rpc; default max_parallelism lowered.
• Node/Fendermint:
  • App hash derived via ABI tuple keccak; expose state_root in StateParams; keep full state history for light client validation.
• Encoding:
  • Add hex (de)serialization for Vec<u8> when human-readable.
• Misc:
  • Small API/field renames and additional test coverage.

^{Written by Cursor Bugbot for commit 92dfd25. This will update automatically on new commits. Configure here.}

[cursor]

Bug: Infinite Loop in App Hash Breakdown Submission

The submit_missing_app_hash_breakdowns method can enter an infinite loop. If query_app_hash_breakdown returns None, next_height isn't incremented, causing the loop to repeatedly query the same height indefinitely.