Make benchmarks operational and clean them up

[gdalle]

• See what they're doing
• Make them compatible with PkgBenchmark.jl
• Run them on CI?

Links:

• https://github.com/JuliaCI/PkgBenchmark.jl
• https://github.com/tkf/BenchmarkCI.jl

[henrik-wolf]

Just for inspiration:

• Makie is running this CI which runs this on every pr.
• CUDA.jl uses buildkite and codespeed to create these very nice dashboards of performance development.

[gdalle]

AAAAAH I JUST REALIZED THAT HENRIK WOLF IS SUPERGROBI