When to set environment variables?

[NoraLoose]

In https://github.com/CWorthy-ocean/C-Star/blob/main/cstar/base/environment.py, we set environment variables. Some of these (in particular CONDA_PREFIX) are not available to RTD. I therefore had to hardcode the following:

C-Star/docs/conf.py

Lines 24 to 25 in fc35204

	# cstar will look for os.environ["CONDA_PREFIX"] but this is not available on RTD; let's fill it with dummy
	os.environ["CONDA_PREFIX"] = str(root)

We should think about whether we can move the setting of environment variables elsewhere, so that this step only happens if you actually want to make a run (this is when the environment variables are supposedly needed?), but not upon importing cstar.

If RTD is the only case in which this logic fails, it's maybe fine, but I can imagine it will fail in other cases as well.

[TomNicholas]

Maybe let's use a context manager, see for example https://docs.xarray.dev/en/stable/user-guide/options.html. Then we could do something like

with cstar.set_environment("roms_marbl"):
    case = Case.from_yaml(...)
    case.setup()
    case.run()

Then we have automatically unset the environment variables at the point the contextmanager is exited.