• Implements is_running() on the Workflow asyncio loop, returning True, so asyncio.get_running_loop().is_running() works inside Workflows instead of raising NotImplementedError.
• This is needed for the LangGraph plugin, because the langgraph package raises this error when run in a Temporal Workflow.

Test plan

• New test_workflow_loop_is_running asserts the loop reports running from inside a Workflow
• Existing Workflow test suite passes
• LangGraph plugin test suite passes