fix: broken multipart processor on windows

[jabdr]

The multipartBodyProcessor is broken on windows, because it creates a temporary file without closing it.

This would usually not be a problem, as the gc would take care of it, but the tests on windows fail, because go test tries to delete the files before gc cleaned the file descriptors.

Windows refuses to delete files as long as the file descriptor is open. Closing the temporary file fixes this issue and go test is able to cleanup the files.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.14%. Comparing base (4ff1f76) to head (c42a842).
Report is 73 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1137      +/-   ##
==========================================
+ Coverage   82.72%   83.14%   +0.42%     
==========================================
  Files         162      164       +2     
  Lines        9080     7688    -1392     
==========================================
- Hits         7511     6392    -1119     
+ Misses       1319     1042     -277     
- Partials      250      254       +4     

Flag	Coverage Δ
default	83.14% <100.00%> (+5.30%)	⬆️
examples	83.14% <100.00%> (+56.71%)	⬆️
ftw	83.14% <100.00%> (+35.77%)	⬆️
ftw-multiphase	83.14% <100.00%> (+33.59%)	⬆️
tinygo	83.14% <100.00%> (+7.73%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.