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_yfinance_stale_ohlcv_guard.py

@@ -13,12 +13,12 @@ import pandas as pd
 import pytest
 
 import tradingagents.dataflows.config as config_module
-import tradingagents.dataflows.y_finance as y_finance
+import tradingagents.dataflows.vendors.yahoo.market as yahoo_market
 import tradingagents.default_config as default_config
 from tradingagents.dataflows import router
 from tradingagents.dataflows.config import set_config
 from tradingagents.dataflows.errors import NoMarketDataError
-from tradingagents.dataflows.stockstats_utils import _assert_ohlcv_not_stale
+from tradingagents.dataflows.vendors.yahoo.ohlcv import _assert_ohlcv_not_stale
 
 
 def _frame(date):
@@ -76,9 +76,9 @@ class StaleGuardPropagationTests(unittest.TestCase):
             def history(self, start, end):
                 return stale
 
-        with mock.patch.object(y_finance.yf, "Ticker", DummyTicker), \
+        with mock.patch.object(yahoo_market.yf, "Ticker", DummyTicker), \
                 self.assertRaises(NoMarketDataError):
-            y_finance.get_YFin_data_online("CB", "2026-06-01", "2026-06-11")
+            yahoo_market.get_YFin_data_online("CB", "2026-06-01", "2026-06-11")
 
 
 @pytest.mark.unit