fix(archiver): guard getL1ToL2Messages against incomplete message sync (backport #21494)

[AztecBot]

Summary

Backport of #21494 to v4-next.

getL1ToL2Messages(checkpointNumber) now throws L1ToL2MessagesNotReadyError if the requested checkpoint's message tree hasn't been sealed on L1 yet (i.e., checkpointNumber >= inbox treeInProgress). This prevents callers from deriving incorrect inHash values from incomplete data.

Conflicts resolved

• errors.ts: The OutOfOrderLogInsertionError class from surrounding context on next does not exist on v4-next — kept only the new L1ToL2MessagesNotReadyError class.
• kv_archiver_store.test.ts: Same — removed OutOfOrderLogInsertionError import that doesn't exist on v4-next.

Test plan

• Build compiles (yarn build)
• kv_archiver_store.test.ts inbox tree guard tests pass (3/3)
• archiver-sync.test.ts all tests pass (32/32)

ClaudeBox log: https://claudebox.work/s/5a11777010141fb0?run=3

[AztecBot]

Automatically closing this stale claudebox draft PR (no updates for 5+ days). Re-open if still needed.