refactor(agents): organise the agents package by what each module holds

- tools.py: the analysts' data tools, previously seven modules under utils
- context.py (was agent_utils, without its tool re-exports), state.py, rating.py and structured.py sit beside schemas.py
- every role package has an __init__

tests/test_signal_processing.py

@@ -6,12 +6,7 @@ header, so the rating is read deterministically; no second model call is made.
 
 import pytest
 
-from tradingagents.agents.utils.rating import (
-    RATING_REVIEW,
-    RATINGS_5_TIER,
-    extract_rating,
-    parse_rating,
-)
+from tradingagents.agents.rating import RATING_REVIEW, RATINGS_5_TIER, extract_rating, parse_rating
 
 # ---------------------------------------------------------------------------
 # Heuristic parser