Set domain on OAuth1 token

[matin]

Whatever domain is being used during the original login is the same one that should continue to be used with the OAuth1 token. This change saves the domain on the OAuth1 token to ensure the correct domain is using when loading from a saved token.

This closes #24, which addresses the issue that caused #21.

This change is fully backwards compatible. The domain is only configured if there's one that's saved. If none is saved, the prior behaviors continues.

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (515933f) 100.00% compared to head (4a55056) 100.00%.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #25   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           29        29           
  Lines         1035      1036    +1     
=========================================
+ Hits          1035      1036    +1     

Flag	Coverage Δ
unittests	100.00% <100.00%> (ø)

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Files	Coverage Δ
garth/auth_tokens.py	100.00% <100.00%> (ø)
garth/http.py	100.00% <100.00%> (ø)
garth/sso.py	100.00% <100.00%> (ø)
garth/version.py	100.00% <100.00%> (ø)
tests/conftest.py	100.00% <ø> (ø)

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