feat(fast-inbox): record the opening L1 block number and hash on each inbox bucket

[spalladino]

Stacked on #25342

Groundwork, no behaviour change. The archiver already knew which L1 block opened each Inbox bucket — every
MessageSent log carries the block number and hash — but only the number reached the persisted bucket snapshot,
and neither field reached the InboxBucket type the archiver serves to the sequencer and the validator.

InboxBucket now carries l1BlockNumber and l1BlockHash (schema included, so they survive the JSON-RPC hop
for out-of-process archivers), and BucketSnapshot persists the hash alongside the number. That is what lets the
next PR ask "is the L1 block that opened this bucket still canonical, and does it have a child?" for the
descendant-confirmed eligibility rule, and what lets the archiver in the message-only stack compare a stored
bucket against the live chain.

Two smaller things came with it:

• The snapshot records the block a bucket was opened in, taken from its first message. The Inbox keys buckets
  by block.timestamp, so on a chain where consecutive blocks can share a timestamp (anvil with manual mining)
  one bucket can span several L1 blocks; that is logged at warn and the opening block is kept. Production
  Ethereum timestamps are strictly increasing, so a bucket there never spans more than one block. The cost of
  recording only the opening block is that a reorg touching only a later co-timestamped block of the same bucket
  is invisible to the hash; both fields say so.
• The archiver's message test doubles now derive a bucket's L1 block from its L1 timestamp rather than from its
  sequence number, with a deterministic, distinct hash per block. Rollover siblings that share a timestamp share
  an L1 block, as on chain, and code that confused a bucket sequence with an L1 block number now fails its tests.

InboxBucketRef, the reference carried on block proposals, is deliberately unchanged: a validator reads the
bucket's L1 block from its own archiver and never from the proposer.

Breaking store format. The bucket snapshot gains a field with no versioning or migration, so an existing
archiver database will not deserialize. That is fine here — this line has never shipped, and dev databases
resync from L1.

Gates: full yarn build, yarn format and yarn lint on the touched packages. Tests: archiver 575/575,
stdlib src/messaging + src/interfaces/archiver.test.ts 118/118, validator-client, sequencer-client
(including the anvil-backed l1_publisher.integration.test.ts), aztec-node
node_public_calls_simulator.test.ts, world-state integration.test.ts. No e2e.

Fixes A-1878