Added `CreateAsync` for bulk entity creation and `UpsertAsync`
and `UpsertSingleAsync` for upsert operations in `IRepository`
and `Repository`. Improved error handling in `UpdateSingleAsync`
and `DeleteSingleAsync` by throwing `NotFoundException` when no
matching entity is found. Refactored `FindAsync` and `UpdateAsync`
for better readability and performance. Cleaned up formatting in
`DeleteAsync`.