add a bbox validator to ensure correct order and valid wgs84 coordinates

[geospatial-jeff]

Adds a bbox validator to ensure order is correct and coordinates are valid WGS84.

Closes #94

[codecov-commenter]

Codecov Report

Merging #95 (5e46c09) into master (45e2735) will increase coverage by 0.12%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #95      +/-   ##
==========================================
+ Coverage   96.06%   96.18%   +0.12%     
==========================================
  Files          20       20              
  Lines         457      472      +15     
==========================================
+ Hits          439      454      +15     
  Misses         18       18              

Flag	Coverage Δ
unittests	96.18% <100.00%> (+0.12%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
stac_pydantic/api/search.py	96.15% <100.00%> (+0.91%)	⬆️

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