[MNT] python 3.14 compatibility and python 3.9 end-of-life

[fkiraly]

• removes support for python 3.9 which has reached end-of-life
• adds support for python 3.14

sktime is not yet compatible with 3.14, this is handled with a condition on python.

(we need to see if anything fails, before merging)

[fkiraly]

on the failing job, it is attempting to install scipy<1.16 - where is that coming from?

[SimonBlanke]

on the failing job, it is attempting to install scipy<1.16 - where is that coming from?

scikit_learn-1.7.0 is installed in the CI. The old scipy version comes from this.

The scikit-learn version 1.7 comes from this line:
https://github.com/SimonBlanke/Hyperactive/blob/main/.github/workflows/test.yml#L137

1.7 apparently stands for ==1.7.0