Extract crates_io_database crate

[Turbo87]

This crate only contains the database schema at the moment, but could be extended with other purely database-related code in the future. This should hopefully help with untangling our mess of interdependencies in the models module.

This might also help a little bit with compile times of the crates_io crate, since all of the table!() macros can be expanded once and can then be cached since the schema does not change that often.

Finally, it would make it possible for other subcrates to depend on the schema, without pulling in all of the other crates_io code.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.71%. Comparing base (5673bdd) to head (2c72b22).
Report is 5 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #9648   +/-   ##
=======================================
  Coverage   88.71%   88.71%           
=======================================
  Files         287      287           
  Lines       29339    29339           
=======================================
  Hits        26028    26028           
  Misses       3311     3311           

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[Turbo87]

alright, looks like no objections, so let's do this :)