Fix debugger colors Escape sequence and off-by-one in #14387

Correctly handle "ipython --matplotlib=<whatever>"

Linting

_matplotlib_manages_backends uses hasattr not version check

Review comments

Reify colors from debugger. (#14387) This help with static checking.

Add tests for resolving backend name and gui loop

Add temporary CI run using matplotlib-inline's entry-point code

Darken and mypy

Move Matplotlib backend resolution to Matplotlib