Implement a comprehensive cache versioning system that allows developers to version their cached function outputs and automatically handle cache migrations when function logic or return schemas change.

Technical Details:

• Add a cache_version parameter to the @cachier decorator
• Store version metadata alongside cached values in all backend cores
• Implement automatic cache invalidation when version changes
• Create a migration framework allowing custom migration functions between versions
• Support semantic versioning (e.g., version="1.2.3")
• Add migrate_cache(old_version, new_version, migration_func) API
• Include backward compatibility mode to read old versions temporarily
• Implement version compatibility checking and warnings

Use Cases:

• Function logic changes requiring cache rebuild
• Data schema evolution over time
• Team collaboration with different code versions
• Production deployments with zero-downtime migrations

Complexity Factors:

• Requires changes to all backend cores (Pickle, MongoDB, Redis, SQL, Memory)
• Schema migration logic for different backends
• Thread-safe migration process
• Rollback mechanisms for failed migrations