Add extraction utility functions

[ZoeLeibowitz]

These functions have been extracted from my PETSc fork. @JDBetteridge wants to use them for something outside of PETSc.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.08%. Comparing base (661939b) to head (47b7463).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2554   +/-   ##
=======================================
  Coverage   92.07%   92.08%           
=======================================
  Files         238      239    +1     
  Lines       47032    47129   +97     
  Branches     4143     4151    +8     
=======================================
+ Hits        43303    43397   +94     
- Misses       3077     3078    +1     
- Partials      652      654    +2     

Flag	Coverage Δ
pytest-gpu-aomp-amdgpuX	72.59% <ø> (ø)
pytest-gpu-nvc-nvidiaX	73.64% <ø> (ø)

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