Replace pyqt requirement with qtpy

[beenje]

Checklist

• Used a personal fork of the feedstock to propose changes
• Bumped the build number (if the version is unchanged)
• Re-rendered with the latest conda-smithy (Use the phrase @conda-forge-admin, please rerender in a comment in this PR for automated rerendering)
• Ensured the license file is being packaged.

The current conda package forces to install pyqt, which is an alias for pyqt5.

PlotPy depends on QtPy to be compatible with different Python-to-Qt bindings.
Allow to install pyqt5, pyqt6 or pyside6 instead of forcing pytqt5.

Note that uses will have to add manually the required Qt binding to their environment.
This is already done like that in pythonqwt-feedstock.

[conda-forge-admin]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipe/recipe.yaml) and found it was in an excellent condition.

[beenje]

The pipeline is failing due to missing distutils which was removed in 3.12.

We only had a warning in previous build:

 │   $SRC_DIR_run_env/lib/python3.14/site-packages/guidata/external/darkdetect/__init__.py:15: DeprecationWarning: distutils Version classes are deprecated. Use packaging.version instead.
 │     if V(platform.mac_ver()[0]) < V("10.14"):

I will open an issue on guidata repo.