Extract Pauli flow from XZ-corrections

[mahbub570]

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Context (if applicable):

Description of the change:

Add XZCorrections.to_pauli_flow + Pattern.extract_pauli_flow (GF(2) rebuild of hidden anachronical X/Y corrections from pattern XZ, not open graph), fix Pauli Pattern.draw flow-from-pattern, tests for round-trip + negatives.

Related issue:
Closes: #432

[codecov]

Codecov Report

❌ Patch coverage is 95.19231% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.01%. Comparing base (8bf1ebe) to head (d542473).

Files with missing lines	Patch %	Lines
graphix/pattern.py	76.92%	3 Missing ⚠️
graphix/flow/core.py	97.80%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #532      +/-   ##
==========================================
+ Coverage   88.85%   89.01%   +0.16%     
==========================================
  Files          49       49              
  Lines        7135     7231      +96     
==========================================
+ Hits         6340     6437      +97     
+ Misses        795      794       -1     

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[thierry-martinez]

Thank you for your contribution. As you may have noticed, another pull request (#526) already addresses the same issue, and a third PR (#534) has been opened in the meantime.

The overall approach of your PR is very similar to that of #526: the Pauli‑flow definition yields a system of GF(2) equations, where the anachronical corrections are the unknowns, and solving this system provides the correction sets.

Could you clarify how your contribution differs from, or improves upon, the previous work? Specifically, please explain why you consider your approach to be better.

[mahbub570]

Ya, it seems others are more perfect then mine 😞

Closing it.