chore(fast-inbox): emit inbox lag and checkpoint cap from the constants generator (A-1434)

[spalladino]

Moves INBOX_LAG_SECONDS (12) and MAX_L1_TO_L2_MSGS_PER_CHECKPOINT (1024) out of the hand-declared file-scope constants in ProposeLib.sol and into the generated Constants library, giving L1 Solidity and the TS node a single source of truth (A-1434, Fast Inbox cleanup).

Both values already lived in constants.nr (the Noir source of truth) and were already emitted to constants.gen.ts; the only gap was the Solidity side, which gates emission behind an allowlist.

• Add both names to the SOLIDITY_CONSTANTS allowlist in constants/src/scripts/constants.in.ts, so yarn remake-constants emits them into ConstantsGen.sol. constants.gen.ts is unchanged (already present).
• Regenerate ConstantsGen.sol (generator output; not hand-edited).
• ProposeLib.sol imports Constants and references the generated values; the hand-declared file-scope copies are deleted.
• Update ProposeInboxConsumption.t.sol to import the constants from ConstantsGen.sol instead of ProposeLib.sol.

TS node code that validates inbox consumption (stdlib cutoff predicate, validator-client streaming checks, sequencer-client bucket selector) already reads these from @aztec/constants, so no TS source change is needed.

Testing:

• forge build and forge test test/rollup/ProposeInboxConsumption.t.sol (15 tests) pass.
• The three TS regression suites pass: stdlib inbox_consumption (10), validator-client streaming_inbox_checks (14), sequencer-client inbox_bucket_selector (9).
• @aztec/constants, @aztec/l1-artifacts, and @aztec/ethereum build.

Part of the Fast Inbox stack, on top of #24784..#24793.