fix fd parsing unquoted attribute values

[KhafraDev]

fixes #4660

claude did ~half of this PR so be wary

[codecov-commenter]

Codecov Report

❌ Patch coverage is 94.21053% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.87%. Comparing base (7cc4fcf) to head (da5192a).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/web/fetch/formdata-parser.js	94.21%	11 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4662      +/-   ##
==========================================
- Coverage   92.87%   92.87%   -0.01%     
==========================================
  Files         106      106              
  Lines       33272    33354      +82     
==========================================
+ Hits        30902    30976      +74     
- Misses       2370     2378       +8     

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[KhafraDev]

Can we land this...? It's a bug fix. I don't know why I'm being asked to microoptimize everything.

[mcollina]

lgtm

[KhafraDev]

this seems to have fixed #4661 as well, great