fix: resolve 6 warning issues from code review

5. Add daily PnL reset loop — UTC midnight auto-reset via
   _daily_reset_loop in main.py, prevents stale daily_pnl accumulation
6. Fix set_base_balance race condition — call once in main.py before
   spawning bots, instead of each bot calling independently
7. Remove realized_pnl != 0 from close detection — prevents entry
   orders with small rp values being misclassified as closes
8. Rename xrp_btc_rs/xrp_eth_rs → primary_btc_rs/primary_eth_rs —
   generic column names for multi-symbol support (dataset_builder,
   ml_features, and tests updated consistently)
9. Replace asyncio.get_event_loop() → get_running_loop() — fixes
   DeprecationWarning on Python 3.10+
10. Parallelize candle preload — asyncio.gather for all symbols
    instead of sequential REST calls, ~3x faster startup

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/test_ml_features.py

@@ -48,7 +48,7 @@ def test_build_features_rs_zero_when_btc_ret_zero():
     btc_df["close"] = 50000.0  # 모든 캔들 동일
     eth_df = _make_df(10, base_price=3000.0)
     features = build_features(xrp_df, "LONG", btc_df=btc_df, eth_df=eth_df)
-    assert features["xrp_btc_rs"] == 0.0
+    assert features["primary_btc_rs"] == 0.0
 
 def test_feature_cols_has_24_items():
     """Legacy test — updated to 26 after OI derived features added."""