[kytta]

Python 3.15 is out now :) We can now test under it and declare support for it

I ran tests locally; all relevant pass

  py315: OK (4.06 seconds)
  py315t: OK (3.06 seconds)
  lint: OK (1.20 seconds)
  congratulations :) (8.36 seconds)

[kytta]

Implemented via #744 instead