feat: add last_updatedsensor for last API call

[firstof9]

fixes #80

[codecov]

Codecov Report

Attention: Patch coverage is 91.66667% with 1 line in your changes missing coverage. Please review.

Project coverage is 84.59%. Comparing base (4a79d68) to head (d47a220).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
custom_components/gasbuddy/__init__.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #125      +/-   ##
==========================================
+ Coverage   84.40%   84.59%   +0.19%     
==========================================
  Files           7        7              
  Lines         404      409       +5     
==========================================
+ Hits          341      346       +5     
  Misses         63       63              

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