controllers/krate/publish: Migrate to diesel-async queries

[Turbo87]

finally...

now, unfortunately we still have a spawn_blocking() call in the endpoint since I didn't feel comfortable with processing the tarball on the async worker thread, but at least we're not using the AsyncConnectionWrapper wrapper anymore 🎉

This will allow us to throw away a bunch of duplicated code in some of the follow-up PRs :)

[codecov]

Codecov Report

Attention: Patch coverage is 96.79144% with 6 lines in your changes missing coverage. Please review.

Project coverage is 88.94%. Comparing base (45040bf) to head (2bad84c).

Files with missing lines	Patch %	Lines
src/controllers/krate/publish.rs	96.75%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10041      +/-   ##
==========================================
- Coverage   89.45%   88.94%   -0.51%     
==========================================
  Files         295      295              
  Lines       31475    31480       +5     
==========================================
- Hits        28156    28000     -156     
- Misses       3319     3480     +161     

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