Replace vulture's dead code check with `coverage.py`?

[joelostblom]

Taking #241 further, we might be able to get rid of vulture even for dead code detection, since coverage.py can do that more reliably than vulture (which we already use with pytest). That would be a bigger change than #241, but since we already use coverage.py, it wouldn't require taking on anything new.

Note that there is also an older discussion of including this in Ruff directly astral-sh/ruff#872. That would be more similar to Vulture since it would parse the AST looking for dead code, rather than running the code like coverage.py

[lwjohnst86]

Hmm, how would coverage do that?

[joelostblom]

I'm unsure too, but this is from Vulture's readme:

coverage finds unused code more reliably than Vulture, but requires all branches of the code to actually be run.

I wonder if it involves actually having a test written for each part of the code or if there is some automatic way for coverage.py to traverse all possible logic paths and see if all code is reachable. I haven't looked into it, just wrote it down based on that it was mentioned in the readme and I wanted to come back to it later.