fix: ensure spack env exists before activation

[plexoos]

Related to #23

[veprbl]

We need to update tokens, it seems. I took liberty to submit to https://eicweb.phy.anl.gov/containers/eic_container/-/merge_requests/1270 for now.

[wdconinc]

This is not necessary. Directories are valid environments. Creating a named environment will place it in a different directory than intended.

[wdconinc]

See https://spack.readthedocs.io/en/latest/environments.html#independent-environments in contrast with https://spack.readthedocs.io/en/latest/environments.html#creating-a-managed-environment

Adding a managed environment with the name $ENV will create it, but it will still be the anonymous environment that is filled and installed in the container.

[plexoos]

Looks like updating the Spack packages repo isn’t possible unless you’re working inside a named environment (see #29).