This PR has a large blast radius because it takes the final step and bumps up the Controller to be fully async.
We have historically done a piece-by-piece update, so all operations were already async but the controller interface was kept synchronous.
With this update, the controller is now fully async and all tests are updated.
Most places where the new C# compiler warns about function names not ending in `Async` were also adressed, giving a massive refactor change.
Functionally, no changes are done.
This PR improves the query used to calculate the size of removed files when issuing the purge-broken-files command.
This PR also adds the option `--reduced-purge-statistics` which will fully skip the size calculation, in the event the query is still performing poorly.
This fixes#6366
Kenneth Skovhede