refactor(dataflows): name the shared modules by what they hold

- interface -> router; symbol_utils -> symbols, which also takes safe_ticker_component
- utils is split: get_current_date to date_window, the HTTP helpers to net
- dataflows imports are absolute; the NoMarketDataError re-export from symbols is gone

tests/test_yfinance_stale_ohlcv_guard.py

@@ -15,10 +15,10 @@ import pytest
 import tradingagents.dataflows.config as config_module
 import tradingagents.dataflows.y_finance as y_finance
 import tradingagents.default_config as default_config
-from tradingagents.dataflows import interface
+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.symbol_utils import NoMarketDataError
 
 
 def _frame(date):
@@ -98,11 +98,11 @@ class StaleGuardRoutingTests(unittest.TestCase):
             )
 
         with mock.patch.dict(
-            interface.VENDOR_METHODS,
+            router.VENDOR_METHODS,
             {"get_stock_data": {"yfinance": _stale}},
             clear=False,
         ):
-            out = interface.route_to_vendor(
+            out = router.route_to_vendor(
                 "get_stock_data", "CB", "2026-06-01", "2026-06-11"
             )
         self.assertIn("NO_DATA_AVAILABLE", out)