Ignore non-finite parsed Max-Age values

[offyotto]

Guard numeric conversion with Number.isFinite. Oversized decimal attributes currently produce ±Infinity and overwrite a prior valid Max-Age. Adds overflow and duplicate-attribute regressions. Verified: 63,743 Vitest cases, TypeScript build/typecheck, 1.27 kB bundle (1.4 kB limit). Independent of serializer validation in #286.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (4898ba2) to head (f1d76f5).
⚠️ Report is 40 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #289   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            1         1           
  Lines          160       195   +35     
  Branches        69        84   +15     
=========================================
+ Hits           160       195   +35     

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