Upstream fixes and tools from Chemfc

[henryleberre]

Description

• Simplify macOS installation using pre-built mpich binaries instead of building open-mpi from source.
• Parallel ./mfc.sh format (@wilfonba).
• Fixed . ./mfc.sh venv command.
• Added t_step_print casefile option. Defaults to 1 and is the frequency at which we print the current t_step to stdout. Useful for simulations with many short timesteps so that your terminal doesn't get filled up.
• Update deprecated checkout@v3 to @v4 in Github actions.
• Add the creation of the <case dir>/equations.dat file in pre_process listing the mappings from cons.X and prim.X variables to their names.
• More robust case.fpp generation.

Type of change

• [x] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)

Scope

• [x] This PR comprises a set of related changes with a common goal

How Has This Been Tested?

• [x] MacOS Sanoma (./mfc.sh test)
• [ ] CI (running)

[sbryngelson]

I didn't know . ./mfc.sh venv existed, what is its purpose/is it documented anywhere?

[henryleberre]

I didn't know . ./mfc.sh venv existed, what is its purpose/is it documented anywhere?

It lets you enter the Python virtualenv (sources the venv into your shell session). I do not foresee a user having to use this.