Import cache fix and revert revert

[mxwli]

Apply import cache fix and revert the initial revert in two separate commits.

It seems that no additional py::module::import calls have been made since the initial revert, so no additional import cache calls are needed.

[acquamarin]

Double check we have replaced every import statemen with import cache

[codecov]

Codecov Report

Attention: Patch coverage is 97.18310% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 93.26%. Comparing base (f4a95ab) to head (3f84585).

Files	Patch %	Lines
...api/src_cpp/include/cached_import/py_cached_item.h	50.00%	1 Missing ⚠️
.../src_cpp/include/cached_import/py_cached_modules.h	95.65%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3025   +/-   ##
=======================================
  Coverage   93.25%   93.26%           
=======================================
  Files        1125     1130    +5     
  Lines       42956    43000   +44     
=======================================
+ Hits        40059    40104   +45     
+ Misses       2897     2896    -1     

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