fix: walk loop and switch bodies in module statement passes

[ryanhill1]

Fixes #354

has_measurements() / remove_measurements() / has_barriers() / remove_barriers() fall back to self._statements when the module has not been unrolled, and the statement walker did not descend into for / while / switch bodies — so an occurrence inside one was invisible and removal was a no-op.

iter_quantum_statements and drop_statements (the walker #345 introduced for box/if) now descend into loop blocks and switch cases/default. The unrolled path is unchanged: loops and switches are fully expanded by unroll() and never reach _unrolled_ast.

Also in this PR:

• Adds regression coverage ensuring barrier removal preserves unrelated operations inside loop bodies.
• Adds while-loop coverage for detecting and removing measurements in nested statements.
• Updates the changelog with the nested loop and switch statement traversal fix.

Nested Statement Removal Flow

sequenceDiagram
  participant BarrierTests as tests/qasm3/test_barrier.py
  participant MeasurementTests as tests/qasm3/test_measurement.py
  participant Module as src/pyqasm/modules/base.py ⚠️
  participant Walker as iter_quantum_statements() ⚠️
  participant Dropper as drop_statements() ⚠️
  participant Changelog as CHANGELOG.md
  BarrierTests->>Module: remove_barriers()
  MeasurementTests->>Module: remove_measurements()
  Module->>Walker: find nested statements
  Module->>Dropper: remove matching statements
  Walker->>Walker: descend into loops and switch cases
  Dropper->>Dropper: descend into loops and switch cases
  Module-->>BarrierTests: preserve unrelated operations
  Module-->>MeasurementTests: remove nested measurements
  Changelog-->>Module: documents traversal update

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 85.71429% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/pyqasm/modules/base.py	85.71%	2 Missing ⚠️

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[ryanhill1]

@Argus-Eye review

[argus-eye]

🔎 Argus · 10/10 — Correctly extends statement passes into loop and switch bodies

🔍 PR intent vs diff (LLM analysis)

Argus read the diff against the stated intent. This is not an execution log — reviewer still needs to test behavior.

Goal: Make module statement passes detect and remove measurements and barriers inside for, while, and switch bodies before unrolling.
Not in scope:

• The unrolled path is unchanged; loops and switches are fully expanded by unroll() and do not reach _unrolled_ast with their bodies intact.
  Stated acceptance criteria (from PR/issue — not independently verified):
• iter_quantum_statements descends into for and while loop blocks and switch cases/default.
• drop_statements descends into for and while loop blocks and switch cases/default.
• has_measurements(), remove_measurements(), has_barriers(), and remove_barriers() handle occurrences inside non-unrolled loop and switch bodies.

✅ Intent delivered

Verdict: This PR adds the intended traversal and removal support for measurements and barriers in non-unrolled loop and switch bodies. It is ready to merge.

💡 2 P2 · 4 files reviewed

Architecture: The recursive traversal keeps module-level statement passes consistent with nested AST structure; broader nested-control-flow coverage would further protect this behavior.

2 findings · 2 inline · 0 folded

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