add libcst as install_requires, print errors to stderr & return 1/0, add pre-commit hook & update config,

[jakkdl]

Didn't come up with any good ways of writing an automated test for pre-commit, but tested it locally and against my fork - and therefore finding the catastrophically bad errors in init & setup 😅
I was a bit surprised missing libcst wasn't picked up by tox, but that's because the testenv depends on hypothesmith - which requires libcst.

We surely want to start tagging releases though, I looked at shed's CI workflow if there were anything there that automatically created tags but didn't find anything so I'm a bit curious if/how you automate that or if you manually do it on releasing.

[jakkdl]

rejigged the tests a bit to have two tests explicitly for SystemExit.

[Zac-HD]

I looked at shed's CI workflow if there were anything there that automatically created tags but didn't find anything so I'm a bit curious if/how you automate that or if you manually do it on releasing.

Automated via this ci config invoking this janky code! It's not pretty, but it works 😅

[jakkdl]

haha that's some beautiful jank! I'll add it in a PR