Improve CI/CD and Compatibility Across Python Versions, Suppress RuntimeWarnings

[maximpavliv]

This pull request expands beyond the original warning suppression to bring the plugin’s test infrastructure and dependencies in line with current DeepLabCut practices and newer Python versions.

⚡️ Improvements and Fixes

• Suppress NaN RuntimeWarnings
  Suppresses the harmless

  RuntimeWarning: invalid value encountered in cast
  

  triggered when keypoint data contain NaNs during label refinement.
  Implemented in __init__.py using Python’s warnings module and scoped to this specific warning only.

• CI/CD Modernization

  • Drop testing for Python 3.9 (PyTables no longer provides wheels for this version).
  • Add testing for Python 3.11 and 3.12.
  • Unbound the PySide6 version requirement (the previously pinned 6.4.2 is unavailable on Python 3.12).
  • Restrict NumPy to >=1.18.5,<2.0.0, matching the main DeepLabCut repository.

• Test Stability

  • Fixed a teardown failure in silently_dock_matplotlib_canvas by returning early if the Window object lacks the _qt_window attribute after tests.
  • Updated CycleEnumMeta.__new__ to accept **kwargs, ensuring compatibility with the boundary keyword introduced in Python 3.11.

These changes ensure clean test runs across Linux, macOS, and Windows on Python 3.10–3.12 and reduce console clutter.