macOS support (for the fancy peeps with nice furniture)

[goodboy]

A more series effort toward #404 and getting macOS running as part of our CI!

There's been some new collabs entering the scene who are helping with this so I will be piecewise making updates here as we work through various fixes on other git-service-platforms.

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Current set of (seemingly) working patches

• (5c79fa8057519876d4d2726fbea2a800496fc740) Use platformdirs for .config.get_rt_dir()