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_ticker_symbol_handling.py

@@ -3,7 +3,7 @@ import unittest
 import pytest
 
 from cli.utils import normalize_ticker_symbol
-from tradingagents.agents.utils.agent_utils import build_instrument_context
+from tradingagents.agents.context import build_instrument_context
 
 
 @pytest.mark.unit