STELLA has zero unit tests or any consistency checks

This issue motivated by a workshop where many of us are attendees, but mesa-stella currently has zero testing for consistency or even compilation, let alone running or giving a good answer. The stella/res/stella_extras.f90 file which Bill wrote to parse output may be deprecated too. I've been meaning to rebuild this, but I'm raising an issue here just so there's an open issue about it.

Start by reviewing the STELLA-related files and the role of stella/res/stella_extras.f90, including whether that file is still used. Define the consistency, compilation, and runtime checks needed before implementing them. Done means STELLA has documented checks that detect failures and confirm a valid result.

Written by the indexing model from the issue text.