PERF: add explicit noexcept qualifiers to resolve perf regressions (Cython 3)

[neutrinoceros]

PR Summary

As tested on my fork, this resolves most of the performance regressions seen in smoke tests with bleeding-edge CI (getting testing airtime from ~17min to ~8 min).

follow up to #4386

[matthewturk]

Am I understanding that our global settings don't propagate to PXD files?

[neutrinoceros]

which global settings ?

[matthewturk]

Oh, I thought you tested it with setting the noexcept globally -- I thought there was a compiloer option to revert to previous settings.

[neutrinoceros]

Disabling exception handling globally is only possible Cython 3, so we can't do that until we drop Cython 0.29. noexcept is backported as a noop to 0.29.x so it is the only option to transition smoothly. I don't want to add it blindly everywhere so instead I'm targeting functions where regressions are seen :)

[matthewturk]

Ah, I understand. I think for some reason I thought we gatekept the opt behind a version check. But this is fine.

[neutrinoceros]

pushed a bunch more noexcept for SelectorObject.select_* routines, which I found were responsible for regressions too.
I'm testing the current state of the branch on my fork at https://github.com/neutrinoceros/yt/actions/runs/4566963443

[neutrinoceros]

This is not over (performance is still degraded on Cython 3.0.0b2), but we're getting there. I'd prefer to keep my PRs small so I'll wait for this one to be included before I dig further.

[matthewturk]

I think one thing that's been slightly unexpected that we're learning here is that some of the inline functions also need the declarations, even though we want them inlined.