Add caching to API Resources

[jacobtomlinson]

Closes #253
Xref #251

Calling kr8s.api_resources() can be an expensive operation, and kr8s.get() calls this under the hood every time. So this PR adds a cache to that call.

It looks like kubectl caches these requests to a file on disk for 10 minutes, which makes sense given that kubectl can't maintain an in-memory cache between separate CLI calls. I considered trying to reuse the cache that kubectl uses, but I feel that ties us too closely to a kubectl implementation detail.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (1a79d2c) 94.56% compared to head (50e69d6) 94.57%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #254      +/-   ##
==========================================
+ Coverage   94.56%   94.57%   +0.01%     
==========================================
  Files          27       27              
  Lines        2743     2749       +6     
==========================================
+ Hits         2594     2600       +6     
  Misses        149      149              

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