chore: support python 3.13

[mwtoews]

Python 3.13 was recently released, which works fine with most of flopy's functionality.

Only VTK (and PyVista) does not yet support Python 3.13 from PyPI, as specified with conditional expressions. All package combinations for Python 3.13 are available for conda-forge.

[mwtoews]

Further checks with conda-forge reveal that not all packages have yet been built for Python 3.13. For instance, shapely and pymetis are not yet available. Thus testing has been removed for now. For reference, use this doc to try and install Python and packages for 3.13.

Nevertheless, local testing on linux works with this PR for PyPI using pip install -e .[test,optional] which installs everything except VTK and PyVista.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.2%. Comparing base (332a310) to head (ffed180).
Report is 1 commits behind head on develop.

Additional details and impacted files

@@            Coverage Diff            @@
##           develop   #2341     +/-   ##
=========================================
- Coverage     74.2%   74.2%   -0.1%     
=========================================
  Files          292     292             
  Lines        59685   59685             
=========================================
- Hits         44335   44334      -1     
- Misses       15350   15351      +1     

see 7 files with indirect coverage changes

[wpbonelli]

I thought we were out of the woods w.r.t. to the recent micromamba/windows issue but evidently not. I will merge anyway.