Add MXX, MYY, MZZ instructions

[rafaelha]

Summary

• Implement MXX, MYY, MZZ two-qubit parity measurement instructions by delegating to the existing MPP infrastructure
• Supports inverted targets and multiple pairs per instruction

This PR also adds support for II_ERROR.

Closes #76

Test plan

• Unit tests for parsing: single pairs, multiple pairs, mixed with other measurements
• Integration tests for sampling: Bell state eigenvalues (XX, YY, ZZ), inverted targets, multiple pairs

🤖 Generated with Claude Code

[github-actions]

PR Preview Action v1.8.1
Preview removed because the pull request was closed.
2026-04-07 02:06 UTC

[github-actions]

☂️ Python Coverage

current status: ✅

Overall Coverage

Lines	Covered	Coverage	Threshold	Status
2169	2096	97%	0%	🟢

New Files

No new covered files...

Modified Files

File	Coverage	Status
src/tsim/core/parse.py	94%	🟢
TOTAL	94%	🟢

updated for commit: aa1ab4c by action🐍

[Copilot]

Pull request overview

Adds support for Stim’s two-qubit Pauli parity measurement instructions (MXX, MYY, MZZ) in Tsim by translating them into equivalent MPP measurements during parsing, and extends the parser to tolerate II_ERROR.

Changes:

• Extend parse_stim_circuit to recognize MXX/MYY/MZZ and delegate each target-pair to mpp(...), including inverted-target parity handling.
• Ignore II_ERROR (and I_ERROR) instructions during parsing.
• Add unit/integration tests and update the overview demo notebook to mention and illustrate the new measurement instructions.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
src/tsim/core/parse.py	Adds parsing support for MXX/MYY/MZZ (via MPP) and ignores II_ERROR.
test/unit/core/test_parse.py	Adds parser-level record-length tests for MXX/MYY/MZZ.
test/integration/test_sampler_circuits.py	Adds sampler integration tests validating deterministic outcomes for Bell/state parity cases, inversion, and multiple pairs.
docs/demos/overview.ipynb	Updates measurement documentation/examples to include MXX/MYY/MZZ and tweaks an MPP example.

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