chore(fast-inbox): circuits cleanup and checkpoint header format (A-1387)

[spalladino]

FI-17 of the Fast Inbox (AZIP-22) stack. Stacked on #24791 (A-1386); it removes the legacy inHash from the checkpoint header now that the consensus flip (#24789, A-1384) has switched validation to the streaming rolling hash. After this PR, inboxRollingHash is the checkpoint's only inbox commitment.

Consensus-format change

• The checkpoint header loses its inHash field across all three preimage layers in lockstep: noir CheckpointHeader (checkpoint_header.nr), TS CheckpointHeader (stdlib/src/rollup/checkpoint_header.ts), and Solidity ProposedHeaderLib (struct + hash packing). The field ordering is otherwise unchanged; the header shrinks by one field (32 bytes: CHECKPOINT_HEADER_SIZE_IN_BYTES 380 to 348, CHECKPOINT_HEADER_LENGTH 14 to 13).
• The header-hash fixtures were regenerated from checkpoint_header.test.ts (the established workflow) and pasted into the noir tests; the p2p golden-byte fixture (wire_compat_fixtures.ts) was refreshed for the checkpoint-proposal serialization, which shrinks by exactly the one removed field. The block-proposal wire fixture is unchanged (block-level inHash is out of scope, see A-1388).

Circuits and constants

• Strips the dead unconstrained in_hash pass-through from the sized InboxParity<S> circuit and ParityPublicInputs (noir + TS + the hand-written noir-protocol-circuits-types conversion wrappers). The circuit is kept (sized-parity, per FI-06's topology decision), so no VK-tree indices move.
• Retires NUMBER_OF_L1_L2_MESSAGES_PER_ROLLUP (replaced everywhere by MAX_L1_TO_L2_MSGS_PER_CHECKPOINT, same value 1024) and the now-dead NUM_MSGS_PER_BASE_PARITY, NUM_BASE_PARITY_PER_ROOT_PARITY, and L1_TO_L2_MSG_SUBTREE_ROOT_SIBLING_PATH_LENGTH. Generated constants (constants.gen.ts, ConstantsGen.sol) were regenerated via remake-constants.
• Deletes FrontierLib.sol and its tests (Parity.t.sol, the Frontier harness and merkle test) now that their last users are gone.

Verification

• Noir: types::checkpoint_header (5/5), rollup_lib::parity and checkpoint_root::parity_tests (15/15), and the checkpoint-root header-assembly path pass locally. The full checkpoint_root suite (68 tests) is too slow to run in full locally and rides CI.
• Solidity: forge test green across Rollup, RollupFieldRange, Inbox, InboxBuckets, RollupGetters (76/76), covering header hashing and the regenerated checkpoint fixtures.
• Jest: checkpoint_header, the p2p wire-compat suites, and the parity/messaging suites pass (43 tests), confirming the fixture regeneration is byte-consistent.
• VK/artifact/Prover.toml regeneration and the generated Noir ABI types ride CI (local yarn build in noir-protocol-circuits-types / simulator / prover-client is expected to fail on stale circuit artifacts until then); e2e and the broken-zone typecheck are the CI-of-record for those.

Stack

Part of the Fast Inbox stack #24784 through #24791 (umbrella #24774): A-1379 (#24784), A-1380 (#24785), A-1381 (#24786), A-1382 (#24787), A-1383 (#24788), A-1384 flip (#24789), A-1385 (#24790), A-1386 (#24791, base of this PR).

Resolves A-1387.

l1 publisher inbox consumption via the streaming selector (CI fix, pass-8)

The A-1387 inHash-removal rewrite left l1_publisher.integration.test.ts hardcoding previousInboxRollingHash = Fr.ZERO and bucketHint = 0n while consuming real L1→L2 messages, so message-consuming checkpoints reverted on L1 with Rollup__InvalidInboxRollingHash / UnconsumedInboxMessages (masked every prior CI round behind earlier failures). INBOX_LAG_SECONDS is an L1-time censorship cutoff, not whole checkpoints, so no checkpoint-depth shift register reproduces the aged bucket set. The test now mirrors the real Inbox buckets into its MockL1ToL2MessageSource and reuses the production selectInboxBucketForBlock (which mirrors ProposeLib.validateInboxConsumption) to pick exactly the buckets each checkpoint must consume, deriving the consumed bundle, the propose bucket hint, and the header rolling hash from that one selection. Box: 13/13, verified at a-1387 and a-1388.