* Implemented ordering for expanded iterators
* Update test_graph_execution_state.py
Added a test for nested iterator execution ordering. (Failing at commit time!)
* Filter invalid nested-iterator parent mappings in _prepare()
When a graph has nested iterators, some "ready to run" node combinations do not actually belong together. Previously, the scheduler would still try to build nodes for those mismatched combinations, which could cause the same work to run more than once. This change skips any combination that is missing a valid iterator parent, so nested iterator expansions run once per intended item.
* Fixed Collect node ordering
* ruff
* Removed ordering guarantees from test_node_graph.py
* Fix iterator prep and type compatibility in graph execution
Include iterator nodes in nx_graph_flat so iterators are prepared/expanded correctly. Fix connection type checks to allow subclass-to-base via issubclass. Harden iterator/collector validation to fail cleanly instead of crashing on missing edges. Remove unused nx_graph_with_data(). Added tests to verify proper functionality.
