Ensure MPIDs are returned by find_structure

[esoteric-ephemera]

Closes #1025 by validating IDs at the end of a call to find_structure

[codecov-commenter]

Codecov Report

❌ Patch coverage is 66.66667% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 67.29%. Comparing base (5ecebec) to head (52956a2).
⚠️ Report is 248 commits behind head on main.

Files with missing lines	Patch %	Lines
mp_api/client/routes/materials/materials.py	66.66%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1026      +/-   ##
==========================================
+ Coverage   66.85%   67.29%   +0.43%     
==========================================
  Files          50       50              
  Lines        2767     2770       +3     
==========================================
+ Hits         1850     1864      +14     
+ Misses        917      906      -11     

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