More caching work, be explicit about paths, use ccache in cibuildwheel

[timkpaine]

As per title, more work to ensure Linux builds in particular are properly caching vcpkg and ccache artifacts.

[timkpaine]

Looks like caches are coming back now for linux:

Will have to see if we can afford to cache per-python or if just caching per os/arch is sufficient.

[ngoldbaum]

I think you need to make the caches per-python-version, otherwise you get errors like this one from the post setup cache step for the python 3.10 run:

Failed to save: Unable to reserve cache with key ccache-ccache-Linux-X64-, another job may be creating this cache. More details: Cache already exists. Scope: refs/pull/28/merge, Key: ccache-ccache-Linux-X64-, Version: 15c80211763d03468c2c9070680654f9264282cf4daa2c6ceac80f2e3eaeb295

[timkpaine]

I think you need to make the caches per-python-version, otherwise you get errors like this one from the post setup cache step for the python 3.10 run:

Failed to save: Unable to reserve cache with key ccache-ccache-Linux-X64-, another job may be creating this cache. More details: Cache already exists. Scope: refs/pull/28/merge, Key: ccache-ccache-Linux-X64-, Version: 15c80211763d03468c2c9070680654f9264282cf4daa2c6ceac80f2e3eaeb295

That shouldn't actually matter as so long as one of them writes it, stuff will be saved. But the compilation relies on python headers, so by not saving per-python we have to recompile more than we would otherwise. The problem with saving per-python is we take up more cache space overall, which increases the likelihood of something we need being evicted.

[timkpaine]

rerunning all jobs to see if these changes had any noticeable effect 😓

[timkpaine]

Seems to be doing the trick but I'm already anticipating some more caching PRs 😅

[ngoldbaum]

Excellent, much faster!