Function make_data_source_dispatcher 

pub fn make_data_source_dispatcher<T>() -> RoleDispatcher
where
    T: DataSourceRuntime + 'static,
    <T as DataSourceRuntime>::Error: Display,

Build a RoleDispatcher for a concrete impl of crate::roles::DataSourceRuntime. Used by Engine::register_*_dispatcher chain (Node::with_<role>(&value)) so single-role components dispatch through the same TypeId-keyed registry as multi-role / Protocol-bearing components.