Reject Expires dates outside cookie year bounds

[offyotto]

Validate UTC years 1601–9999 before serialization. Year 0049 currently round-trips as 2049; years above 9999 exceed the four-digit cookie-date grammar. Adds eight rejection cases and three valid-boundary controls. Verified: npm test (63,751 cases), TypeScript build/typecheck, 1.28 kB bundle. RFC 6265 §§4.1.1, 5.1.1.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (4898ba2) to head (3069805).
⚠️ Report is 40 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #290   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            1         1           
  Lines          160       197   +37     
  Branches        69        86   +17     
=========================================
+ Hits           160       197   +37     

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