feat: Add support for -x/--exclude-lines.

[DanCardin]

Attempts to fix #26

I integrated the regex matching into the line-inclusion loop (Thus it works by excluding excluded lines from the total set), but it occurred to me afterwards, that it could perhaps instead be integrated similarly to _add_unseen_source_files. There, you're already scanning a bunch of files, compiling them, and adding their lines. It could work in reverse, where it scans all the files, compiles them, and adds matching lines to the "seen" set.

I'm not familiar enough with the code to know if one would make more or less sense than the other, but I think the way I have it implemented now is at least intelligible and seems to be performant.

I tried to defer imports to expensive modules (like re/inspect) up to the point of the exclude_lines feature being utilized. I dont see any slowdown when not making use of the feature, but a ~0.2s slowdown when making use of the feature on a ~6s test run (~10k LOC, since I figure it scales worse with numbers of code objects scanned).

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I wasn't able to get all the tests running locally, it seems unrelated to my changes, and that it might be some environment specific thing that I'm not sure what I need to do; but I can't say for certain.

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Also, I dont love this feature being purely given by command line options. if you're into this feature, i would ideally like to follow it up by (even optional) reading from pyproject.toml for a tool.slipcover setting (for this at a minimum)

[DanCardin]

without this cache, I saw a ~2s slowdown relative to the current impl.

5.9s without exclusions
6.1s with exclusions and cache
8.8s with exclusions no cache
10.5s with coverage

[jaltmayerpizzorno]

Hi, thank you for your pull request! Please check out my questions and/or make the changes requested.

[DanCardin]

Sorry, I think my original commit must have had some editor auto-formatting or something going on. I definitely was not consciously going through and removing annotations and altering those version-constrained blocks! Updated to be (hopefully now) only the actual changes related to the enhancement.