build(bench): pin GDC identities and evidence contracts

[DecisionNerd]

Objective

Provide shared benchmark-owned manifests, dataset provenance, reference handling, and evidence schemas for independent GDC suites.

Requirements

• Pin GDC/spec, generator, and driver versions or commits.
• Verify checksums and record licenses/acquisition without committing bulk data.
• Keep every suite independently selectable and reported.
• Sanitize evidence and preserve reproducibility metadata.

Acceptance criteria

• Validation rejects incomplete provenance.
• Fixtures cover checksum mismatch, missing assets, reference mismatch, and drift.
• Adapters share contracts without sharing workload semantics.

BDD completion scenario

Given a GDC profile
When inputs are acquired
Then every generator, driver, dataset, and reference has an immutable recorded identity.