Replace conformance manifest with Biosiglib lock

[dcajal]

Summary

• replace conformance.json with a one-line biosiglib.lock
• make the normal MATLAB suite validate the lock and pinned checkout
• simplify conformance, propagation, release, caching, and contributor documentation

Why

Conformance is total for merged code. The repository only needs to record the exact Biosiglib commit it tests; support states and duplicated metadata create a misleading second model.

Biosiglib pin

• 13303c6ca909867fcb43b9c7858d62eeb7a05df5 (Replace conformance manifests with commit locks biosiglib#86)

Validation

• 256 MATLAB tests
• MkDocs strict build
• workflow YAML parsing
• git diff --check