Updated docstring for generate_mirror_circuits

[jordandsullivan]

Updated docstring for generate_mirror_circuits to reflect accurate return types

Description

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License

• I license this contribution under the terms of the GNU GPL, version 3 and grant Unitary Fund the right to provide additional permissions as described in section 7 of the GNU GPL, version 3.

Before opening the PR, please ensure you have completed the following where appropriate.

• I added unit tests for new code.
• I used type hints in function signatures.
• I used Google-style docstrings for functions.
• I updated the documentation where relevant.
• Added myself / the copyright holder to the AUTHORS file

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.22%. Comparing base (8b9ba75) to head (69efc6b).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2353   +/-   ##
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  Coverage   98.22%   98.22%           
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  Files          87       87           
  Lines        4056     4059    +3     
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+ Hits         3984     3987    +3     
  Misses         72       72           

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[cosenal]

We can say A tuple of a randomized mirror circuit of type return_type, and the correct bitstring.
I left a comment in #2344: what's the meaning of correct here?