Add aggregate logical observable groups

[masa10-f]

Summary

• add PauliFrame.logical_observable_groups() to expand every indexed logical-observable seed through the dependent-chain closure
• update Stim export to consume the aggregate logical-observable API, matching the existing detector_groups() flow
• preserve the existing raw seed storage and per-group API for backward compatibility
• document the new public API in CHANGELOG.md

Why

Detector groups already have an aggregate closure-expanded accessor, while logical observables required callers to iterate over raw seeds and invoke the per-group method themselves. This API asymmetry made logical observables appear to behave differently even though both use the same closure algorithm.

Impact

Patterns and .ptn files can now expose all closure-expanded logical observables with one call:

pattern.pauli_frame.logical_observable_groups()

Existing callers of logical_observables and logical_observables_group() remain compatible.

Validation

• uv run ruff check graphqomb/pauli_frame.py graphqomb/stim_compiler.py tests/test_pauli_frame.py
• uv run --extra stim pytest -q -s tests/test_pauli_frame.py tests/test_stim_compiler.py tests/test_ptn_format.py (92 passed)
• git diff --check

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.38%. Comparing base (f18a5e6) to head (073364c).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #239   +/-   ##
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  Coverage   86.38%   86.38%           
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  Files          31       31           
  Lines        5111     5112    +1     
  Branches      908      908           
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+ Hits         4415     4416    +1     
  Misses        491      491           
  Partials      205      205           

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