Add the ability to opt out of (into?) coverage reporting when collecting observability data

[hgoldstein95]

I'm experiencing significant slowdown (~10x at least) when collecting observability data vs. not. At first I thought the data collection itself was slow, but even a no-op TESTCASE_CALLBACK causes the performance degradation. I was able to narrow the issue down to tracing; if this if-statement is disabled, performance returns to normal.

I think this kind of performance hit is expected for coverage measurement, and that's fine in a lot of cases, but Tyche needs to operate in a pretty tight feedback loop. Can we add a flag that makes coverage measurement optional?

[Zac-HD]

#3776 means collecting coverage info should be pretty fast on CPython 3.12+, but I'd be happy to add another environment variable and make the _trace_obs calculation a bit more complicated. Want to open a PR?

[hgoldstein95]

Just made one! (Hopefully I did it right). #3826

[tybug]

Looks like this can be closed with the above pr 👍