controllers/krate/publish: Reduce spawn_blocking() scope

[Turbo87]

Quite a bit of code that is currently within the spawn_blocking() scope isn't using the sync database connection, so we might as well move it outside. One notable exception is the process_tarball() call, which stays within a dedicated spawn_blocking() call for now. While process_tarball() is operating on in-memory bytes and should be fairly fast, we sometimes process multiple megabytes of data here, so we can't rely on this being fast enough for an async thread.

Best reviewed in "ignore whitespace changes" mode 😉

[codecov]

Codecov Report

Attention: Patch coverage is 94.35484% with 7 lines in your changes missing coverage. Please review.

Project coverage is 89.18%. Comparing base (d3106cd) to head (6abdc3d).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/controllers/krate/publish.rs	94.35%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10003      +/-   ##
==========================================
- Coverage   89.19%   89.18%   -0.01%     
==========================================
  Files         295      295              
  Lines       30752    30758       +6     
==========================================
+ Hits        27428    27433       +5     
- Misses       3324     3325       +1     

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