Fix beam heating and OpenMP options

[wtbarnes]

This pull request contains two major bugfixes:

1. Add full support for parallelized runs with OpenMP (Fixes Setting use_openmp to True results in compilation error because of missing CHUNK_SIZE #163, Fixes OpenMP support  #152)
2. Fixes a bug when using the beam heating option by adding the BEAM_HEATING directive to the necessary header file.

Additionally, this PR also contains a few other more minor fixes:

1. The compiler script is now configured at runtime. This makes it easier to specify a compiler besides g++. Flags (e.g. for optimization) can also be optionally passed in.
2. The run_shell_command function now just takes in a path (Fixes Simplify run_shell_command function #162)
3. There are now a few additional tests for running HYDRAD with different options. These are just "smoke tests" to ensure that certain combinations of config parameters don't lead to unexpected behavior.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (52a9666) 66.85% compared to head (5a96f65) 68.48%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #164      +/-   ##
==========================================
+ Coverage   66.85%   68.48%   +1.62%     
==========================================
  Files          11       11              
  Lines         694      714      +20     
==========================================
+ Hits          464      489      +25     
+ Misses        230      225       -5     

Files	Coverage Δ
pydrad/configure/configure.py	84.21% <100.00%> (+3.62%)	⬆️
pydrad/configure/util.py	89.65% <100.00%> (+1.72%)	⬆️

... and 1 file with indirect coverage changes

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