Add Support for FREEZing In-Memory Parts for Backups

Why it matters

This feature addresses the limitation where FREEZE only captured parts already flushed to disk, excluding in-memory parts. By supporting freezing of in-memory parts, users can create more comprehensive backups, ensuring that all recent data, including data still in memory, is included.

How to use it

Users can perform a FREEZE operation as usual on their tables. The system now automatically includes in-memory parts in the freeze process, so no additional configuration is required beyond executing the FREEZE command.