Fix for optional matplotlib

[sbrunner]

fix #634

[Copilot]

Pull Request Overview

This pull request addresses issue #634 by modifying the matplotlib import strategy to make matplotlib an optional dependency. The changes remove top‐level runtime imports of matplotlib modules, move one import into the TYPE_CHECKING block, and update a type annotation to use a forward reference for optional dependency handling.

• Removed runtime imports of matplotlib.axes and matplotlib.projections.polar.
• Added a TYPE_CHECKING-only import for matplotlib.projections.polar.
• Updated a type annotation for PolarAxes to a string literal for lazy evaluation.

Comments suppressed due to low confidence (1)

deskew/init.py:15

• Consider adding an inline comment here to clarify that this import is used exclusively for type checking, which supports the optional dependency handling strategy.

    import matplotlib.projections.polar