fix: refactor qubit types into new submodule

[rmshaffer]

Issue #, if available:

Description of changes:
Cleans up GlobalQubitRegister to properly encapsulate its usage of oqpy.Qubit. Moves qubit-related type definitions into a new submodule under types.

Testing done:

Merge Checklist

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (748c91e) to head (7608573).

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #110   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           52        53    +1     
  Lines         2289      2310   +21     
  Branches       265       267    +2     
=========================================
+ Hits          2289      2310   +21     

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