Add contract_definition as single source of truth for check metadata

[Jamestth]

Summary

• Previously CheckResult metadata selectively cherry-picked contract definition fields (description, dimension, severity, type, unit), meaning new ODCS schema fields (e.g. tags, customProperties, authoritativeDefinitions) were silently dropped.
• This fix attaches the full raw ODCS quality entry as metadata["contract_definition"] — the single source of truth for all contract fields, without any filtering or editing.
• Computed/derived fields (check_path, target, operator, is_generated, engine, etc.) remain at the top level of metadata, clearly separated from contract data.
• Renames ambiguous metadata fields for clarity:
  • schema → schema_name (avoids confusion with DB schema)
  • rule → rendered_implementation (covers both SQL query and custom implementation after vowl transforms)

Breaking changes

• metadata["schema"] → metadata["schema_name"]
• metadata["rule"] → metadata["rendered_implementation"]
• metadata["description"], metadata["dimension"], metadata["severity"], metadata["type"], metadata["unit"] removed from top-level metadata — now accessible via metadata["contract_definition"]["description"] etc.
• CSV/DataFrame export columns reflect these renames and now include all contract fields (e.g. tags, businessImpact)