Class equivalence pass: contract harness + fixtures

[iahncajigas]

Summary

• keeps class contract harness and fixture-generation plumbing committed
• removes tracked class-equivalence report/log artifacts from the repository
• updates tests to generate class-equivalence inventory/report at runtime (or skip when MATLAB reference checkout is unavailable)
• updates parity workflows to generate and upload class-equivalence inventory/report as CI artifacts

Public hygiene change

Class-equivalence reports/logs are produced as CI artifacts and are no longer committed under parity/.

Validation

• pytest -q passes locally
• class equivalence report generation, functional parity gate, example output spec, and numeric drift checks pass locally