feat(graph): run the analysts at the same time (#1255)

- each analyst is a graph of its own (model and tools on a private message history) that returns only its report; all start together and the research debate waits for every report
- the message-clearing nodes are gone; a checkpoint saved by the sequential layout starts fresh
- TradingAgentsGraph.stream_run streams the analysts' messages for debug mode and the CLI, whose status and timing now track the analysts side by side

tests/test_checkpoint_resume.py

@@ -210,6 +210,10 @@ class TestCheckpointSignature(unittest.TestCase):
         # Stable for identical inputs.
         g.config = {"max_debate_rounds": 1, "max_risk_discuss_rounds": 1}
         self.assertEqual(base, g._run_signature("stock"))
+        # A checkpoint saved by the sequential layout is not resumed on the
+        # parallel one: its pending node no longer exists, and the join would
+        # never fire.
+        self.assertIn("analysts=parallel", base)
 
 
 if __name__ == "__main__":