Speed up CI

[boeschf]

• use Cmake's Ninja backend for building Arbor
• use ccache for storing build artifacts
  • unique cache key: needs to reflect os, compiler, shared/static variant and CPU vector extensions (avx, avx2, etc)

[brenthuisman]

Hurray: https://github.com/arbor-sim/arbor/actions/runs/3321531860/jobs/5490065274

[boeschf]

well, the ninja stuff runs
the error came because I tried to additionally use ccache - and I am pretty sure it is due to the cache key not including the CPU architecture / SIMD vector length

[brenthuisman]

The key might need to be specific for each config in the matrix. Reading the docs, I think job_id might be that unique string. [Update] On second thought, no I don't think so. Can't find a better way than ${{matrix.name}}-${{matrix.os}}-....

[thorstenhater]

Nice. I am going to merge this and after the CI is through fold this into #1958 to check whether we get the weird behaviour.

[thorstenhater]

Nice job. We should -- for the future -- investigate whether we can factor out some part of the .yml.