Function to_rust_accumulator 

pub fn to_rust_accumulator(accum: Py<PyAny>) -> AccumulatorFactoryFunction

Wrap a Python accumulator factory in an AccumulatorFactoryFunction.

Retained for downstream callers that previously consumed this helper to build a AccumulatorFactoryFunction for create_udaf or similar factory-based APIs. New in-crate code should construct a [PythonFunctionAggregateUDF] directly so the codec can downcast and ship it inline.