Function duckdb_add_scalar_function_to_set 

pub unsafe extern "C" fn duckdb_add_scalar_function_to_set(
    set: duckdb_scalar_function_set,
    function: duckdb_scalar_function,
) -> duckdb_state

Adds the scalar function as a new overload to the scalar function set.

Returns DuckDBError if the function could not be added, for example if the overload already exists.

@param set The scalar function set @param function The function to add