Expose Rust stabilizer-code distance search and verification workflow to Python

[ciaranra]

Summary

The incremental-weight distance search in pecos-qec (calculate_distance, find_min_weight_logicals_with_info, CSS modes) and the StabilizerCodeSpec verification machinery were fully implemented in Rust but had no Python bindings and no callers. This PR exposes them, giving Python users a supported replacement for the legacy pecos.analysis.VerifyStabilizers development workflow.

New in pecos.quantum:

• StabilizerCodeSpec: hand construction, from_stabilizer_code(...), plus getters for stabilizers, destabilizers, and paired logical operators. str(spec) prints an [[n, k]] summary with all generators.
• StabilizerCodeSpec.builder(n): check(op), logical_z(op), logical_x(op), and three build modes — build(), build_verified() (errors name the exact anticommuting generator pair), and build_with_discovered_logicals() (derives paired logicals and destabilizers via stabilizer simulation).
• spec.distance(max_weight=None, css=False) returning DistanceResult, and spec.min_weight_logicals() returning operators with logical-equivalence info ("X0*Z1"). The search grows error weight from 1, so cost scales with the distance rather than with qubit count, reaching codes the existing StabilizerCode.distance() coset enumeration (capped at k + rank <= 30) cannot.
• Xs, Ys, Zs multi-qubit Pauli helpers, so checks read as Zs([0, 1]) * Y(2).

Removed: pecos/tools/fault_tolerance_checks.py and pecos/tools/stabilizer_verification.py, byte-identical dead copies of the pecos.analysis modules; pecos.tools has been a deprecation shim re-exporting pecos.analysis and these files were unreachable through the public path.

pecos.analysis.VerifyStabilizers itself is left untouched; retiring it and updating the legacy rst docs are follow-ups once this API has settled.

Verification

• cargo test -p pecos-qec: all unit, integration, and doc tests pass.
• New binding tests (17) cross-check the weight search against StabilizerCode.distance() as an exact oracle on the Steane, five-qubit, and Shor codes, and confirm found operators are genuine logicals via syndrome checks.
• A parity test replays the full docs/examples/stab_code_verification.rst storyline: the invalid check set is rejected with a genuinely anticommuting pair identified, the corrected set yields a [[10, 3, 2]] code, and the final set yields [[10, 1, 3]].
• just build-debug, full binding test files (32 passed), and whole-repo just lint all clean.