GXS: Fix "Mark all as read" lag & UI freezes

[jolavillette]

GXS: Fix "Mark all as read" lag & UI freezes

This PR was entirely created by Gemini
At the moment this PR is for testing purpose only
If you are willing to test, notice that "mark all as read/unread" in channels/forums/boards is much faster

Here is what gemini says about the changes:
GXS: Fix "Mark all as read" lag & UI freezes

• Performance: Implemented updateMessageMetaData batching with single SQL transaction and in-memory cache updates, making mass updates instant.
• Stability: Added SQLITE_BUSY retry loop in RetroDb read operations to prevent failures during concurrent writes.
• UI Fix: Grouped mass update notifications in RsGenExchange to prevent event loop starvation and UI freezes.

Code by Gemini