Implemented cached version of generate_oas_component()

[Bartvaderkin]

I tried this after-hours and it works surprisingly well so I cleaned it up and put it here:

It caches generate_oas_component() calls that are repeated multiple times, like when they are part of a TestCase.setup() or some other often re-used code like the MockAPIData class.

It works by using some funky python hash() code to get a cache key and deepcopy() to isolate each usage.

Also it's obviously a memory hole, but memory and deepcopy() are a lot cheaper then CPU cycles running the OAS/faker stack.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (443973e) 94.80% compared to head (6d608cb) 94.80%.
Report is 7 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #972      +/-   ##
===========================================
- Coverage    94.80%   94.80%   -0.01%     
===========================================
  Files          857      858       +1     
  Lines        30068    30133      +65     
===========================================
+ Hits         28507    28567      +60     
- Misses        1561     1566       +5     

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[stevenbal]

Code looks good 👍. Does it make the tests faster as well?