use default depot + julia -O0 flag

[juliasloan25]

Purpose

I also added climacoupler-ci to the Clear Depot pipeline. Now we can use the generic clear depot instead of the coupler-specific one (which I'll delete soon). The default clear depot can be used to clear this pipeline's depot by setting the environment variable slug=climacoupler-ci.

Also minimized optimization of everything in the regular CI by passing the -O0 flag (as opposed to the default -O2 optimization level).

For timing examples, see CI runs with -O0 vs default. The largest change is in GPU CMIP, which goes from 42 to 28 minutes. Some slabplanet runs and the sea breeze experiment become slower because they're run for 1+days. This option seems to only be useful for tests and experiments that run for "a few" steps (maybe <5, depending on the configuration).

[imreddyTeja]

I wonder if this improvement is big enough to make it worth not using julia-actions/julia-runtest@v1, and instead manually running tests like is done here

[juliasloan25]

I was thinking about that too. I'm not sure if there's really any benefit to using julia-actions/julia-runtest. For ClimaCoupler though, most of the test time is dominated by `experiments/ClimaEarth/runtests.jl, which we call manually. But I think that would have a bigger impact in e.g. ClimaLand