Create PyMatching decoder plugin

[bmhowe23]

This PR introduces a PyMatching decoder plugin to the CUDA-Q QEC library.

Ref: https://github.com/oscarhiggott/PyMatching

Summary

The new PyMatching decoder plugin integrates the PyMatching library into the CUDA-Q QEC framework. It allows users to decode syndromes using MWPM by simply requesting the decoder by name. The implementation handles the conversion of a parity check matrix into a PyMatching graph, supporting both standard edges (between check nodes) and boundary edges.

Key Changes

• MWPM Decoder Plugin: Implemented a new decoder in libs/qec/lib/decoders/plugins/pymatching/pymatching.cpp.
• Supports error_rate_vec as a parameter to define edge weights based on physical error rates.
• Maps the PyMatching merge_strategy options (disallow, independent, smallest_weight, keep_original, replace) to CUDA-Q QEC Plugin options.

Tests

• C++ Unit Tests:
  • libs/qec/unittests/decoders/pymatching/test_pymatching.cpp
• Python:
  • libs/qec/python/tests/test_decoder.py
  • libs/qec/python/tests/test_sliding_window.py