Add minimal pyproject.toml

[mss]

My setuptools knowledge is a bit rusty, especially when it comes to how to use the entry points while developing.

This change adds a minimal pyproject.toml which makes a call like uv run gql-cli ... available.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (57ef910) to head (fc63483).
Report is 7 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #514   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           30        30           
  Lines         3102      3127   +25     
=========================================
+ Hits          3102      3127   +25     

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[leszekhanusz]

Thanks, should have done this years ago.