fix(http): handle empty Cookie headers

[dennisimoo]

Fixes #7320.

Treat an empty Cookie header like a missing header and ignore empty cookie pairs, including trailing semicolons. Preserve nonempty values and existing malformed-key validation.

Regression tests cover empty headers, empty pairs, whitespace, and malformed keys. The new trailing-semicolon test failed before the fix.

Tests: deno test -A --doc http/ — 479 passed, 987 steps, 2 ignored. Full lint, formatting and browser checks passed. The earlier full deno task ok run was killed (exit 137) in the unrelated CBOR test that allocates a 4–8 GiB buffer, including on a serial retry.

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.04%. Comparing base (01fe755) to head (ff38944).
⚠️ Report is 10 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7328      +/-   ##
==========================================
- Coverage   95.04%   95.04%   -0.01%     
==========================================
  Files         618      620       +2     
  Lines       51746    52016     +270     
  Branches     9402     9452      +50     
==========================================
+ Hits        49181    49437     +256     
- Misses       2022     2031       +9     
- Partials      543      548       +5     

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[bartlomieju]

Thanks for the PR, it looks mostly okay. I'm still wary that it will throw on a=1; - can you handle that case before we merge the PR?

[dennisimoo]

Handled in ff38944. Empty cookie pairs are now skipped, including a=1;, while malformed nonempty keys still throw. Added regression coverage; all 479 HTTP tests, lint, formatting and browser checks pass.