fix(http): handle empty Cookie headers

[dennisimoo]

Fixes #7320.

Treat an empty Cookie header like a missing header. Whitespace-only values are already normalized by Headers. Nonempty cookies still use the existing parser and validation.

Added a regression test for empty and whitespace-only headers, including the null-prototype return value. It fails before the fix.

Tests: deno test -A --doc http/ — 478 passed, 987 steps, 2 ignored. Lint, formatting and browser checks passed. The 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]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.04%. Comparing base (01fe755) to head (9865e34).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7328   +/-   ##
=======================================
  Coverage   95.04%   95.04%           
=======================================
  Files         618      618           
  Lines       51746    51746           
  Branches     9402     9403    +1     
=======================================
  Hits        49181    49181           
  Misses       2022     2022           
  Partials      543      543           

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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?