add support for python 3.15

[Pavel Zwerschke (pavelzw)]

No description provided.

[Pavel Zwerschke (pavelzw)]

ci is red with

Error:   × failed to solve requirements of environment 'py315' for platform 'osx-arm64'
  ├─▶   × failed to solve the environment

  ╰─▶ Cannot solve the request because of: python 3.15.* cannot be installed because there are no viable options:
      └─ python 3.15.0rc1 | 3.15.0rc2 | 3.15.0rc3 would require
         └─ _python_rc *, for which no candidates were found.
      The following packages are incompatible
      └─ python 3.15.* cannot be installed because there are no viable options:
         └─ python 3.15.0 is excluded because the package is uploaded after the cutoff date of 2026-10-09 09:05:48

tomorrow i can merge this