Fixes a bug in deriving the electron pressure from conserved quantities in AMR files

[wtbarnes]

This fixes a bug in how the electron pressure is calculated from the conserved quantities calculated in the amr files. I was dividing by $\gamma - 1$ instead of multiplying so in cases where only the amr files were being used, the electron temperature was off by over a factor of 2. 🤦

This also includes several tests to ensure this doesn't happen again.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.35%. Comparing base (c175a02) to head (0e45287).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #199      +/-   ##
==========================================
+ Coverage   81.20%   81.35%   +0.15%     
==========================================
  Files          21       21              
  Lines        1096     1105       +9     
==========================================
+ Hits          890      899       +9     
  Misses        206      206              

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[jwreep]

Looks good to me! Relatively simple fix to a simple issue.