Fix ConstrainedReschedule barrier handling

[TSS99]

Summary

Fix ConstrainedReschedule so compiler directives such as barriers are not rejected during rescheduling. Fix #16135.

Details

The Rust implementation now treats directives as unconstrained operations, matching the pass documentation and the previous Python behavior. Unknown non-directive operations still raise the existing error.

Tests

• .venv/bin/python reproducer_issue_16135.py
• .venv/bin/python -m unittest test.python.transpiler.test_scheduling_padding_pass.TestSchedulingAndPaddingPass.test_constrained_reschedule_accepts_barrier
• .venv/bin/python -m unittest test/python/transpiler/test_scheduling_padding_pass.py
• .venv/bin/black --check test/python/transpiler/test_scheduling_padding_pass.py
• .venv/bin/ruff check test/python/transpiler/test_scheduling_padding_pass.py
• cargo fmt --check
• cargo clippy -p qiskit-transpiler --lib --features cache_pygates -- -D warnings
• .venv/bin/reno -q lint

Notes

Full test suite and full tox -elint were not run.

I reviewed the diff and can explain the changed condition and regression test.

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[coveralls]

Coverage Report for CI Build 25501265948

Coverage increased (+0.05%) to 87.682%

Details

• Coverage increased (+0.05%) from the base build.
• Patch coverage: 1 of 1 lines across 1 file are fully covered (100%).
• 36 coverage regressions across 5 files.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

36 previously-covered lines in 5 files lost coverage.

File	Lines Losing Coverage	Coverage
crates/qasm2/src/parse.rs	18	96.68%
crates/circuit/src/parameter/symbol_expr.rs	8	73.93%
crates/qasm2/src/lex.rs	8	92.03%
crates/circuit/src/parameter/parameter_expression.rs	1	91.04%
crates/transpiler/src/passes/unitary_synthesis/decomposers.rs	1	94.71%

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Coverage Stats

Relevant Lines:	122062
Covered Lines:	107027
Line Coverage:	87.68%
Coverage Strength:	963038.28 hits per line

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💛 - Coveralls