feat: archiver syncs Inbox buckets (A-1379)

[spalladino]

Part of the Fast Inbox stack (AZIP-22). Makes the archiver track the L1 Inbox rolling-hash buckets introduced in A-1377, validate the full-width consensus rolling-hash chain, and expose the bucket queries the sequencer/validator will consume (A-1382/A-1383). Purely additive: the legacy per-checkpoint getL1ToL2Messages path is unchanged.

What's added

• InboxMessage gains inboxRollingHash: Fr, bucketSeq, and bucketTimestamp (the L1 block timestamp that keys the bucket). mapLogInboxMessage propagates them; the ethereum MessageSent log now also carries the emitting L1 block's timestamp.
• MessageStore persists a per-bucket snapshot ({ inboxRollingHash, totalMsgCount, timestamp, msgCount, lastMessageIndex }) keyed by bucket sequence, plus a timestamp→sequence index for at-or-before lookups. Snapshots are written as messages are inserted and rewound (deleted / boundary-bucket recomputed) on reorg removal, all inside the existing kv-store transactions.
• addL1ToL2Messages now validates the full-width consensus rolling hash (updateInboxRollingHash) alongside the legacy 128-bit keccak chain. Both run until the streaming inbox flips on (A-1388 removes the legacy one).
• Three queries on L1ToL2MessageSource (implemented by the archiver, supported by the mock, exposed over the archiver RPC schema): getLatestInboxBucketAtOrBefore(timestamp), getInboxBucket(seq), and getL1ToL2MessagesBetweenBuckets(fromExclusive, toInclusive). New InboxBucket type + zod schema in stdlib messaging.

Notes

• No migration: ARCHIVER_DB_VERSION is bumped 7 → 8, so nodes resync their L1→L2 messages from L1. Archiver message stores are rebuildable from L1, so this is acceptable on this release line.
• Folds in A-1344: InboxMessage.l1BlockNumber is widened from UInt32 to UInt64 (the serialization was being rewritten anyway).
• Field naming: the full-width hash is inboxRollingHash: Fr to match the updateInboxRollingHash mirror, CheckpointHeader.inboxRollingHash, and the decoded MessageSent event — the value is a truncated-sha256-to-field element. (The plan's provisional consensusRollingHash: Buffer32 predates the implemented event.) The legacy rollingHash: Buffer16 stays until A-1388.

Out of scope

• Reorg-driven bucket invalidation (a reorg that replays the identical message leaves but re-buckets them across different L1 blocks changes neither the 128-bit nor the full-width leaf-based hash, so localStateMatches cannot detect it, and the allowed message-reinsertion path leaves its bucket snapshot stale). This is handled by A-1389, and bucket consumption is gated off by the streamingInbox flag pre-flip.
• Sequencer/validator consumption (A-1382/A-1383), proposal bucket-reference types (A-1381), and removing the legacy 128-bit hash (A-1388).

Testing

• message_store.test.ts: bucket snapshotting (multi-message, cross-batch, rollover), full-width chain-mismatch detection, reorg rewinding, and the three queries incl. boundary cases.
• archiver-sync.test.ts: end-to-end sync now exercises the full-width chain validation and asserts the bucket queries against the synced state (the fake L1 state mirrors the on-chain bucket assignment).
• stdlib archiver interface RPC round-trip tests for the three new methods.