[WIP] Lazy loading

[esoteric-ephemera]

Expanding scope of lazy loading to:

• Lazily load a rester for an endpoint only when it is inspected
• Lazily initialize a rester only when it is called

Some usage examples for the LazyImport class in tests/core/test_utils.py for how it can be used beyond just the resters

[codecov-commenter]

Codecov Report

❌ Patch coverage is 88.60759% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 63.44%. Comparing base (a8210aa) to head (73e9a50).

Files with missing lines	Patch %	Lines
mp_api/client/core/utils.py	87.80%	5 Missing ⚠️
mp_api/client/routes/molecules/molecules.py	71.42%	2 Missing ⚠️
mp_api/client/core/client.py	90.00%	1 Missing ⚠️
mp_api/client/mprester.py	90.90%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1044      +/-   ##
==========================================
- Coverage   66.83%   63.44%   -3.39%     
==========================================
  Files          50       50              
  Lines        2801     2681     -120     
==========================================
- Hits         1872     1701     -171     
- Misses        929      980      +51     

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