[repo meta] formatting & addition of `pre-commit` configuration

[whi-tw]

Disclaimer: This could be a massive over-step, so please feel free to tell me to stay in my lane.

Working on ercf.py in #150, I noticed that the file had quite a lot of formatting quirks, which I was constantly fighting with in my IDE.

I have reformatted the file with the latest version of black and also removed a lot of trailing whitespace.

Additionally I've added configuration for pre-commit which could potentially prevent things from getting messy again. I've only run it on ercf.py so far, hopefully if people use the pre-commit hook in future, everything will gradually be tidied up. pre-commit can be run locally (docs on the website above) and automatically for free with a CI check via https://pre-commit.ci/ (requires setup on @EtteGit's side).