feat(dex): create DEX dataflows directory structure

Initial DEX data provider directory structure for migration
from TradingAgents (stock) to DEXAgents (crypto).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tradingagents/dataflows/dex/__init__.py

@@ -0,0 +1,8 @@
+"""DEX Data Providers for TradingAgents."""
+try:
+    from .coingecko_provider import CoinGeckoProvider, get_coin_ohlcv, get_coin_info
+
+    __all__ = ["CoinGeckoProvider", "get_coin_ohlcv", "get_coin_info"]
+except ImportError:
+    # Coingecko provider will be added in Task 2
+    __all__ = []