- Implemented `CombinedPersistenceShellFeatureBase` for unified configuration of EF Core persistence components.
- Added `SharedPersistenceSettings` for shared configuration across multiple persistence shell features.
- Updated shell features for SQL Server, MySQL, PostgreSQL, SQLite, and Oracle to use a unified persistence approach.
- Refactored `PersistenceShellFeatureBase` to enable fallback to shared settings.
