Add keyring store for API keys

[chidiwilliams]

No description provided.

[codecov]

Codecov Report

Merging #411 (7e0119f) into main (49a3151) will increase coverage by 0.20%.
The diff coverage is 87.05%.

@@            Coverage Diff             @@
##             main     #411      +/-   ##
==========================================
+ Coverage   78.81%   79.02%   +0.20%     
==========================================
  Files          21       25       +4     
  Lines        2030     2150     +120     
==========================================
+ Hits         1600     1699      +99     
- Misses        430      451      +21     

Flag	Coverage Δ
Linux	79.02% <87.05%> (+0.45%)	⬆️
Windows	?
macOS	?

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Impacted Files	Coverage Δ
buzz/gui.py	76.37% <72.22%> (-0.34%)	⬇️
buzz/store/keyring_store.py	80.95% <80.95%> (ø)
buzz/widgets/general_preferences_widget.py	85.71% <85.71%> (ø)
buzz/widgets/line_edit.py	87.50% <87.50%> (ø)
buzz/widgets/openai_api_key_line_edit.py	100.00% <100.00%> (ø)
buzz/widgets/preferences_dialog.py	100.00% <100.00%> (ø)
...uzz/widgets/shortcuts_editor_preferences_widget.py	79.16% <100.00%> (ø)

... and 2 files with indirect coverage changes

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