Fixes#9644.
Rewrites `db.Iterate` so that it performs DB queries in this format:
- First: `SELECT ...columns... FROM table ORDER BY id LIMIT ...buffer-size...`
- Subsequent buffer fills: adding a `WHERE id > ...last-id-from-previous...`
This approach:
- Prevents records from being missed or returned twice
- Returns records in a predictable order
- Should be faster, by virtue of using database indexes on the primary key to perform the query
- Doesn't rely on any unpredictable database behaviour when using `LIMIT` and `OFFSET` without an `ORDER BY`
- (Downside: does require reflection to read field values off Go structures for the primary key value)
Expands the automated tests to include the predicted failure case identified in #9644, which verified the previous broken behaviour, as well as verifying that the `cond` parameter is applied which was previously not covered by test automation.
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/9657
Reviewed-by: Earl Warren <earl-warren@noreply.codeberg.org>
Co-authored-by: Mathieu Fenniak <mathieu@fenniak.net>
Co-committed-by: Mathieu Fenniak <mathieu@fenniak.net>
