[playground] Add Reset button (#17236)
## Summary
Add a *Reset* button to both Ruff's and Red Knot's playground that
resets the playground to its initial state.
Closes https://github.com/astral-sh/ruff/issues/17195
## Test Plan
https://github.com/user-attachments/assets/753cca19-155a-44b1-89ba-76744487a55d
https://github.com/user-attachments/assets/7d19f04c-70f4-4d9e-b745-0486cb1d4993
