Improvement: Restrict MPI to version 3.0 or higher

[holke]

Closes #1999

Describe your changes here:

Restrict MPI to be version 3.0 or higher.
3.0 is now over 15 years old and we can expect users to have it available.
3.0 introduced shared memory which we use a lot and knowing that it is available (b/c we enforce >=v3.0) make the code much more maintainable.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.60%. Comparing base (98ffe9d) to head (c6f5315).
⚠️ Report is 13 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1998   +/-   ##
=======================================
  Coverage   76.60%   76.60%           
=======================================
  Files         109      109           
  Lines       18721    18721           
=======================================
  Hits        14341    14341           
  Misses       4380     4380           

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