TODO: auto-timestamps
- SaveXyz should set created_at and updated_at; shouldn't touch is_deleted or deleted_at
- if soft delete is enabled, DeleteXyz should do update (not delete) and set is_deleted and deleted_at
- SaveXyz shouldn't set created_at in the do-update branch
- DeleteXyz should have pointer receiver
- GetXyzByID should include `ErrItemIsDeleted` if item is soft-deleted

TODO: primary-key
- SaveXyz shouldn't set primary key if it's rowid

TODO: foreign-key
- Generated types should match foreign keys to the type of the column they point to

TODO: modified-timestamps
- set updated_at and created_at in SaveXYZ
- soft delete option