[FEAT] Add postCommitmentsSafe — idempotent variant

[roeezolantz]

Summary

Adds postCommitmentsSafe to CommitmentRegistry — an idempotent counterpart to postCommitments that silently skips handles already committed under the given version, instead of reverting the entire batch with CommitmentAlreadyExists.

postCommitments (strict) is unchanged; this is purely additive.

Why

Callers like blockchain-poster (CoFHE) batch many handles into one tx. The same handle can appear across batches because:

• FHE outputs are deterministic — repeated operations on the same input produce the same handle
• RabbitMQ redeliveries (after relayer/network failures) can re-batch the same messages

Under postCommitments, the first duplicate reverts the whole batch → nack-requeue → retry → revert again → eventually DLQ. Slim-listener's block tracker stalls. With postCommitmentsSafe, already-committed handles are skipped, the batch progresses, and the on-chain end state is identical.

Tracks PRO-300.

What's reverted/preserved

• Reverts in postCommitmentsSafe:
  • EmptyBatch, LengthMismatch, VersionNotActive, OnlyPosterAllowed — caller bugs / lifecycle violations
  • ZeroCommitHash — indicates upstream bug producing invalid input
• Skipped silently: a handle already mapped under (version, handle) in storage

Observability

New event:

event CommitmentsPostedSafe(bytes32 indexed version, uint256 newlyPosted, uint256 skipped);

newlyPosted + skipped == handles.length. Lets dashboards distinguish "real" commitments from idempotent re-posts.

Tests

13 new tests in CommitmentRegistry.behavior.ts covering:

• Fresh batch — all written, skipped=0
• Re-post identical handle — kept original, newlyPosted=0, skipped=N
• Mixed batch (some new, some existing) — only new ones written
• Within-batch duplicates — first wins, rest skipped
• All four "still revert" cases (zero hash, empty batch, length mismatch, inactive version, non-poster)
• handlesByVersion doesn't double-count on re-posts

All 87 tests pass (pnpm hardhat test).

Test plan

• CI green
• Coordinated rollout with cofhe (blockchain-poster) PR that flips its ABI call to postCommitmentsSafe

Follow-up

Once merged + redeployed, the consuming PR in cofhe (PR #676 — feat/blockchain-poster-event-completion) bumps the submodule SHA and switches blockchain-poster/src/abi.rs to call postCommitmentsSafe.