doc: Documents existing parseCookie behavior

[saripovdenis]

Summary

Documents existing parseCookie behavior when a custom decode returns undefined.

When decode returns undefined, parseCookie skips that value. If the same cookie name appears later, the later value can be used.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (4898ba2) to head (add4def).
⚠️ Report is 25 commits behind head on master.

Additional details and impacted files

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  Coverage   100.00%   100.00%           
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  Files            1         1           
  Lines          160       256   +96     
  Branches        69       114   +45     
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+ Hits           160       256   +96     

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[blakeembrey]

Thanks for the PR, but this a vague undocumented feature that allows someone to skip a value in favor of a second one. It should have test coverage, would you be interested in adding that instead?

[blakeembrey]

We can also document undefined behavior, I think that's preferable to total correctness and a perf hit in the fast path.

[saripovdenis]

We can also document undefined behavior, I think that's preferable to total correctness and a perf hit in the fast path.

oops, added it back and documented!