fix: reject timestamps above sortable range

[gt12889]

Closes #29

Summary

• Reject decoded timestamps above SORTABLE_TIME_MAX in getTimestamp.
• Let getTimestampOrThrow surface the malformed-ID error through its existing path.
• Add regression coverage and update the Date-boundary expectation required by the sortable range contract.
• Document the behavior under Unreleased.

Verification

• npm test — 116 passed.
• npm run typecheck — passed.
• Touched files pass Prettier.
• npm run verify reaches the repository-wide format gate but is blocked by 28 pre-existing unformatted files outside this change.

[suhailopensource]

Thanks for the PR @gt12889 . code LGTM !