Consider simplifying default model_key_prefix

[abrookins]

Summary

The default model_key_prefix currently includes the full module path (e.g., myapp.models.User), which can be problematic:

1. Fragile to refactoring - Moving a model file or renaming a module breaks existing Redis keys
2. Verbose keys - Keys become unnecessarily long
3. Inconsistent with SQL ORMs - Most ORMs use just the class name for table names

Current behavior

class User(HashModel):
    name: str

# Keys look like: myapp.models.User:abc123

Proposed behavior

class User(HashModel):
    name: str

# Keys would look like: User:abc123

Considerations

This is a breaking change that requires careful handling:

• Existing keys would become orphaned after upgrade
• Two models with the same class name in different modules would collide
• Need migration path or documentation for users upgrading

Prior work

PR #522 attempted this change but was closed due to staleness. The implementation was simple (just use __name__ instead of __module__.__name__), but the migration/breaking change concerns need to be addressed.

Options

1. Major version bump with clear migration docs
2. Opt-in flag to use simplified prefix (non-breaking)
3. Keep current behavior but improve documentation (Document model_key_prefix usage #364)