ci(c): enable CCache for builds

[lidavidm]

The builds are reasonably quick right now, but we should play nice with shared resources.

[assignUser]

The issue is that the actions/cache action is broken for use with ccache as caches are immutable, so no updates on primary cache hit. The only way around this is to invalidate the cache every time via a unique key (kind of defeating the idea of a cache...). This works but a repo is limited to 10G of caches at a time, so it can increase eviction and cache misses.

The same thing is an issue over in arrow and I am looking into a solution atm. Due to PRs (correctly) not having secret access using sccache seems not to be possible. There might be a way to use a read-only sccache though and only update it when running CI on push (with secret access)

[lidavidm]

Hmm, thanks for the context. I guess it's not worth pursuing here yet (or rather, there is much lower-hanging fruit in terms of CI and such)