Remove crates.downloads column

[Turbo87]

This PR builds on top of #8232. It switches the backend code to use the crate_downloads table for all downloads queries, and it subsequently drops the obsolete crates.downloads column.

This should be deployed separately from #8232!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.60%. Comparing base (4065b2b) to head (7aca8d3).

❗ Current head 7aca8d3 differs from pull request most recent head 5613d70. Consider uploading reports for the commit 5613d70 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8233      +/-   ##
==========================================
- Coverage   87.88%   87.60%   -0.28%     
==========================================
  Files         270      272       +2     
  Lines       26092    26324     +232     
==========================================
+ Hits        22931    23062     +131     
- Misses       3161     3262     +101     

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[eth3lbert]

I haven't started reviewing this PR yet. However, I noticed that index-related migration seems to be missing. If this is intentional, I think it would be helpful to include a comment in the migration script explaining the rationale behind this decision.

[bors]

☔ The latest upstream changes (presumably 0c0ced7) made this pull request unmergeable. Please resolve the merge conflicts.

[Turbo87]

I noticed that index-related migration seems to be missing. If this is intentional

good catch, that was indeed not intentional. but I just noticed that dropping the column automatically seems to remove the associated index. I guess you were asking about the down.sql that needs to add the index again?

[eth3lbert]

Yes, and we should also consider adding an index on crate_downloads because there are sortings by downloads.

p.s. The index (downloads, crate_id) leads to an index only scan. An index (downloads) would result in an index scan.

[Turbo87]

@eth3lbert I've added the create index calls to the down.sql of the second migration

I think this is ready to go now 🤔

[eth3lbert]

🎉 LGTM 👍