… guards

Catch up with recent GLOAS (EIP-7732) spec changes and add beacon API support:

Spec fixes:
- HighestBidKey: add ParentBlockRoot to prevent cross-fork bid interference (PR #5001)
- Envelope ByRange/ByRoot: add MinEpochsForBlockRequests serve range lower bound (PR #4950)
- Ancestor(): return PENDING for block.slot <= slot, use getParentPayloadStatus for traversal

Beacon API (7 new endpoints):
- POST /beacon/execution_payload_bid — submit bid via BidService + gossip
- GET /validator/execution_payload_bid/{slot}/{builder_index} — query highest bid
- POST /validator/duties/ptc/{epoch} — PTC committee assignments
- GET /validator/payload_attestation_data/{slot} — attestation data for PTC
- POST /beacon/pool/payload_attestations — submit via AttestationService + gossip
- GET /beacon/pool/payload_attestations — query from LRU cache
- GET /beacon/execution_payload_envelope/{block_id} — query envelope from forkchoice

Safety:
- Nil guard for SignedExecutionPayloadEnvelope.Message in applyEnvelope/validateEnvelope
- Nil guard for BlobKzgCommitments in publishBlindedBlocks (GLOAS blocks use bid)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>