Handle image stats through background processing

[jeawhanlee]

Is your feature request related to a problem? Please describe.
Currently the stats processing logic has some complex queries which runs on the main thread and is render blocking.

Describe the solution you'd like
We need to port this logic from the main thread to run in the background instead. See details here and in the following comments.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.

[MathieuLamiot]

Discussio about flaws in the approach here: https://wp-media.slack.com/archives/CU0F6EGQ1/p1734535227194059