Granularize artefact creation; saving environments should be separate opt-in

[h-vetinari]

Debugging at a distance is never fun, but sometimes we need to inspect the artefacts built in a PR (potentially with failing CI) locally.

However, this process is much more cumbersome than it needs to be, chiefly because at every step of the way (in the case of failing CI), the corresponding environments get packaged as well. In the case of conda-forge/tinygrad-feedstock#7, this means that the vast majority of the time is spent packaging the environments

And if I then want to download just the artefact that failed its tests (~3-4MB), I now need to download and unpack 1GB.

Of course, there can be cases where the environments need to be inspected too, but at least in my case, I've never needed to inspect the environments yet, so any artefact interaction with them is just wasted time/bandwidth etc.

For this reason, I think store_build_artifacts: should either default to "only the packages" (with a separate knob store_build_environments: for the environments), or we should turn it into an enum where the choice can be made between none/only-pkg/pkg&env