Drop support for Python 3.7

[tomvothecoder]

Description

• Closes Drop support for Python 3.7 #185

Summary of Changes:

• Remove typing_extensions from setup.py and conda env dependencies
• Update imports from typing_extensions to typing
• Remove Python 3.7 from CI build matrix

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules

If applicable:

• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass with my changes (locally and CI/CD build)
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have noted that this is a breaking change for a major release (fix or feature that would cause existing functionality to not work as expected)

[codecov-commenter]

Codecov Report

Merging #187 (360bbc9) into main (201a575) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main      #187   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            8         8           
  Lines          381       418   +37     
=========================================
+ Hits           381       418   +37     

Impacted Files	Coverage Δ
xcdat/__init__.py	100.00% <100.00%> (ø)
xcdat/axis.py	100.00% <100.00%> (ø)
xcdat/bounds.py	100.00% <100.00%> (ø)
xcdat/dataset.py	100.00% <100.00%> (ø)
xcdat/spatial_avg.py	100.00% <100.00%> (ø)
xcdat/xcdat.py	100.00% <100.00%> (ø)

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