cache cleaning script

[Clément Robert]

Hi everyone,

For everyone that didn't follow my recent work closely, there were a couple test pollution issues with the new cache discovery system, which are now fixed (both on main and 8.0.0b1). If you ran astropy's test suite locally at some point in the previous weeks, it's possible that your system has a couple generated (empty) directories lying around. To amend myself, I'm sharing the following self-contained CLI script I used while working on said fixes, which should hopefully clear any remnants of your local runs.

It has a dry mode and a nuclear option to erase everything. Call it with `--help` to choose how you want to run it.

Here it is: https://gist.github.com/neutrinoceros/acb9e72a1fa5b2b1fce87c915c32bc08

cheers

Clément