Add lru_caches

[gadomski]

Related Issue(s):

• Closes Cache results #101

Description:
The LRU caches are only applied to functions that return fully-fetched values (e.g. an ItemCollection), not applied to generators. This limits the number of places the cache can be used.

PR Checklist:

• Code is formatted
• Tests pass
• Changes are added to the CHANGELOG

[codecov-commenter]

Codecov Report

Merging #167 (2c0133c) into main (dbdc3a4) will increase coverage by 0.20%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #167      +/-   ##
==========================================
+ Coverage   81.00%   81.20%   +0.20%     
==========================================
  Files           9        9              
  Lines         558      564       +6     
==========================================
+ Hits          452      458       +6     
  Misses        106      106              

Impacted Files	Coverage Δ
pystac_client/client.py	79.36% <100.00%> (+0.67%)	⬆️
pystac_client/item_search.py	88.52% <100.00%> (+0.19%)	⬆️

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[gadomski]

@philvarner sorry to re-request review, but I forgot max_size on one of the decorators, and wanted to make sure you were ok with setting to 1 for all four usages.