fix: resource warnings

[gsakkis]

Description

• Fix ResourceWarning from unclosed UploadFile instances
• Fix ResourceWarning in run_server fixture
• Report all warnings as errors unless explicitly silenced

Closes #3835

[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 9 lines in your changes missing coverage. Please review.

Project coverage is 98.35%. Comparing base (69181fd) to head (4f185c7).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
litestar/_multipart.py	58.33%	2 Missing and 3 partials ⚠️
litestar/_kwargs/extractors.py	77.77%	1 Missing and 1 partial ⚠️
litestar/datastructures/upload_file.py	0.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3838      +/-   ##
==========================================
- Coverage   98.40%   98.35%   -0.05%     
==========================================
  Files         344      344              
  Lines       15467    15485      +18     
  Branches     1701     1707       +6     
==========================================
+ Hits        15220    15230      +10     
- Misses        118      122       +4     
- Partials      129      133       +4     

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[cofin]

LGTM

[github-actions]

Documentation preview will be available shortly at https://litestar-org.github.io/litestar-docs-preview/3838