UX: Update counters and covers in the background

[tschechniker]

I have a library of about 150K of photos. Even with an optimized MariaDB every Approve/Archive Batch action takes about 4 seconds. I debugged and found that from these 4 seconds 3.5 seconds are used to regenerate counters. This can easily be done in the background.

Now if i move a photo to the archive it takes milliseconds again 😄

Acceptance Criteria:

• Features and enhancements must be fully implemented so that they can be released at any time without additional work
• Automated unit and/or acceptance tests are mandatory to ensure the changes work as expected and to reduce repetitive manual work ( already there )
• Frontend components must be responsive to work and look properly on phones, tablets, and desktop computers; you must have tested them on all major browsers and different devices
• Documentation and translation updates should be provided if needed
• In case you submit database-related changes, they must be tested and compatible with SQLite 3 and MariaDB 10.5.12+

[CLAassistant]

All committers have signed the CLA.

[lastzero]

@tschechniker Thank you so much! I apologize for not getting back to you sooner. Unfortunately, I've only just noticed this great suggestion.

However, while it seems like a generally good idea to update counters and covers in the background, it might affect the frontend in unexpected ways - so I'd rather not merge this without having time to properly test it. We'll make sure it doesn't get forgotten (again)! ⚠️

[lastzero]

@tschechniker Thanks again for your contribution! Based on your proof-of-concept, the above commit updates counters and covers in the background where possible. I will therefore go ahead and close this PR as it is no longer needed.

I'm very sorry we couldn't get this released sooner. 😞