refactor(dataflows): group the vendors under dataflows/vendors

- vendors/yahoo: ohlcv (loader and cache), market (prices, indicators), fundamentals (profile, statements, insider), news, snapshot
- vendors/alpha_vantage is a package; sec_edgar, fred, polymarket, reddit and stocktwits sit beside it
- the one-method StockstatsUtils class is a function; the duplicate Yahoo host constant is gone
- tests are named after the modules they cover: test_ohlcv_date_column, test_yahoo_snapshot, and the ohlcv and snapshot aliases

tests/test_no_data_handling.py

@@ -14,9 +14,10 @@ from unittest import mock
 import pandas as pd
 import pytest
 
-from tradingagents.dataflows import router, stockstats_utils
+from tradingagents.dataflows import router
 from tradingagents.dataflows.config import set_config
 from tradingagents.dataflows.errors import NoMarketDataError
+from tradingagents.dataflows.vendors.yahoo import ohlcv
 
 
 @pytest.mark.unit
@@ -33,16 +34,16 @@ class TestLoadOhlcvNoPoison(unittest.TestCase):
 
     def test_empty_download_raises_and_does_not_cache(self):
         empty = pd.DataFrame()
-        with mock.patch.object(stockstats_utils.yf, "download", return_value=empty), \
+        with mock.patch.object(ohlcv.yf, "download", return_value=empty), \
                 self.assertRaises(NoMarketDataError):
-            stockstats_utils.load_ohlcv("FAKE", "2026-01-01")
+            ohlcv.load_ohlcv("FAKE", "2026-01-01")
         # Nothing should have been written to the cache.
         self.assertEqual(os.listdir(self._tmp), [])
 
         # A second call must re-attempt the fetch (no poisoned cache served).
-        with mock.patch.object(stockstats_utils.yf, "download", return_value=empty) as dl2:
+        with mock.patch.object(ohlcv.yf, "download", return_value=empty) as dl2:
             with self.assertRaises(NoMarketDataError):
-                stockstats_utils.load_ohlcv("FAKE", "2026-01-01")
+                ohlcv.load_ohlcv("FAKE", "2026-01-01")
             self.assertTrue(dl2.called)