Add a "new regressions" column to the Hardware listing page

Part of #1972.

## Summary

Add a "New regressions" column to the Hardware listing page, showing the count of new regressions per row.

## Acceptance criteria

- [ ] The Hardware listing shows a new-regressions column with an accurate count.
- [ ] No noticeable increase in listing load time from the added data.

Start at the Hardware listing page and trace how each row's existing data is loaded, then identify the source of the new-regressions count. Add the column without causing a noticeable load-time increase, and verify that every row displays an accurate count against the issue's acceptance criteria.

Written by the indexing model from the issue text.