ci: add coverage to pull requests

[github-actions[bot]]

Package	Line Rate	Health
.	53%	➖
analysis	37%	❌
archive	72%	➖
channelml	55%	➖
lems	46%	❌
neuron	31%	❌
neuron.analysis	0%	❌
plot	47%	❌
povray	0%	❌
sbml	91%	✔
sedml	94%	✔
swc	8%	❌
tellurium	0%	❌
tune	0%	❌
utils	62%	➖
xppaut	0%	❌
Summary	37% (2783 / 7609)	❌

[sanjayankur31]

@pgleeson does this look OK to merge to enable coverage?

It only runs coverage for py3.12, and the same comment is updated each time. It's also only enabled for PRs, not for pushes.

I also made lots of fixes to make ruff happy---most of them were genuine issues.

[sanjayankur31]

@lej0hn @AdityaBITMESRA : FYI^, if you notice any issues, please do point them out.

[sanjayankur31]

Merging this, haven't noticed any fall out (yet).