Improve Top Downloaded Apps to use last 24 months aggregation

[qzMalekuz]

This PR updates the Top Downloaded Apps UI to use aggregated
download data from the last 24 months using ReleaseDownloadsByDate.

• Uses ORM aggregation (Sum over count)
• Preserves ordering via Case/When
• Does NOT modify the existing downloads field
• Does NOT change desktop behavior
• Scoped to UI display only (per issue Improvement on Top Downloaded Apps #112)

Let me know if you would prefer the logic structured differently.
Related to #112

[coleslaw481]

Could you add unit tests to apps/tests.py to verify this change works. thanks

[coleslaw481]

Also there is another pull request someone else did on 112: #113
which one makes more sense to merge?

[qzMalekuz]

I’ve added the requested unit tests in apps/tests.py (TopDownloadedAppsTestCase), and all tests are passing successfully.

This implementation aggregates download counts from ReleaseDownloadsByDate over the last 24 months using Django ORM (Sum). Since download history is stored in ReleaseDownloadsByDate, aggregating from this model ensures the ranking reflects downloads within the specified time window rather than relying on the lifetime downloads field, which makes more sense.

This approach also avoids modifying the existing downloads field and keeps the change limited to the UI ranking logic, aligning with the current data model.

Thank You.