Fix unnecessary DAG version churn when DAG file paths change

[kaxil]

When DAG files are loaded from paths that change between deployments (e.g., versioned directories), the python_callable_name in serialized DAGs changes even when the actual DAG code is unchanged.

This happens because qualname() includes the module name, which contains a hash derived from the file path via get_unique_dag_module_name(). When the path changes, the module name changes, causing:

1. Different python_callable_name values
2. Different dag_hash
3. New SerializedDagModel entries on every deployment

Solution

Add exclude_module parameter to qualname() that returns only the qualified name without the module prefix:

# Before: "unusual_prefix_abc123_dag_file.my_function"
qualname(func)

# After: "my_function"  
qualname(func, exclude_module=True)

Use this in operator serialization to ensure python_callable_name is stable across deployments.