refactor: modularize event loop node class methods and helpers

core/framework/graph/event_loop/__init__.py

@@ -0,0 +1,6 @@
+"""EventLoopNode subpackage — modular components of the event loop orchestrator.
+
+All public symbols are re-exported by the parent ``event_loop_node.py`` for
+backward compatibility.  Internal consumers may import directly from these
+submodules for clarity.
+"""