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 88.23529% with 2 lines in your changes missing coverage. Please review.

Project coverage is 98.42%. Comparing base (dcae3b3) to head (af78e6c).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
litestar/datastructures/upload_file.py	0.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3838      +/-   ##
==========================================
- Coverage   98.42%   98.42%   -0.01%     
==========================================
  Files         333      333              
  Lines       15348    15350       +2     
  Branches     1694     1694              
==========================================
+ Hits        15107    15108       +1     
- Misses        111      112       +1     
  Partials      130      130              

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[cofin]

LGTM

[github-actions]

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