newville/wxmplot: 2026.1..0

avoid errors when cursor x/y is None add jupyter notebook example more tests for robust adding of highlight area improve support for dark-mode, including automatically adapting color schemes of configuration panels. set default theme to 'auto', which will use 'dark' when the system is using Dark Mode, and 'light' when not. drop support for Python 3.9 add dependency on wxutils 2026.1.0 and more heavily rely on dark_detect