Add support for Python 3.13

[himoto]

Checklist

• Appropriate tests were added
• Any code changes were done in a way that does not break public API
• All documentation related to code changes were updated
• The new code follows the
  contributor guidelines, in particular the SciML Style Guide and
  COLPRAC.
• Any new documentation only uses public API

Additional context

Since numba v0.61 is available, diffeqpy can be tested with Python 3.13.

[ChrisRackauckas]

Is this actually required?

[himoto]

Not necessarily required, but I wanted to test if the CI would pass with the latest Python version (3.13) to ensure compatibility.

[ChrisRackauckas]

I see. Might as well.