Add ZX-calculus backend

[nabe98]

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Then, please fill in below:

Context (if applicable):

• Add ZX-calculus backend ZXGraphState used for MBQC pattern simplification
• Refs
  • Quantum 5, 421 (2021).
  • EPTCS 384, pp. 203-219 (2023).

Description of the change:

• Implement ZXGraphState operations for local complement, pivot, Clifford removal, phase-gadget conversion, YZ-node merges, and a full_reduce pipeline, with helpers like _clifford_rules, _update_connections, and complete_graph_edges.
• Added to_zx_graphstate to convert a canonical GraphState instance into the ZXGraphState instance while preserving inputs, outputs, and measurement data
• Ship an executable example (examples/zxgraph_simplification.py) that demonstrates simplifying a random circuit’s ZX-diagram and visualizes the states before/after full_reduce

Related issue:
close #102

[masa10-f]

@nabe98
Reminder: Please verify the functionality with a numerical test, comparing the simulated result with the circuit.

[codecov]

Codecov Report

❌ Patch coverage is 82.07792% with 69 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.70%. Comparing base (4c26208) to head (69ffb37).
⚠️ Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #103      +/-   ##
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+ Coverage   76.00%   78.70%   +2.70%     
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  Files          21       23       +2     
  Lines        2209     2555     +346     
  Branches      378      452      +74     
==========================================
+ Hits         1679     2011     +332     
+ Misses        456      455       -1     
- Partials       74       89      +15     

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[masa10-f]

@nabe98 I'll review your PR this weekend. Before that, please move local_cliffords stuff into ZXGraphState since only ZX Calculus uses that attribute, and we want GraphState to be a simple structure.

[nabe98]

I’ll have it revised by Friday night. Thank you in advance.