Full chainstate compaction can take minutes on large databases.
Move `CCoinsViewDB::CompactFull()` to a named `utxocompact` one-shot background thread so validation only schedules the work.
When validation selects compaction after a full flush, the chainstate was just written and another write is less likely to be needed immediately.
The coins view destructor waits for completion, and a mutex prevents compaction from using `m_db` while `ResizeCache()` replaces it.
Co-authored-by: Andrew Toth <andrewstoth@gmail.com>
Github-Pull: #35465
Rebased-From: 394e473d42
1907b3f56c