Make nb_page_inconsistencies in QemuSnapshotCheckResult public

[saruman9]

Description

See #3465 for details.

Checklist

• I have run ./scripts/precommit.sh and addressed all comments

[saruman9]

I've discovered an alternative method to verify the fast snapshot state by comparing the result of the check_fast_snapshot method with QemuSnapshotCheckResult::default(). However, having access to the actual count of inconsistent pages through the nb_page_inconsistencies field could still be valuable for more detailed diagnostics and debugging.