fix: resolution-safe timestamp in trackD_timing resample (pandas 2.x datetime64[ms])

- combination study: PORT LF4h (BTC+ETH) Sharpe 1.32 DD 12.3% remains best
- RV ETH/BTC market-neutral sleeve is genuinely uncorrelated (~0.05) but too weak
  (Sharpe 0.27) to raise portfolio Sharpe; combining the two TF configs is redundant
  (same-asset cross-config corr 0.80)

scripts/research/trackD_timing.py

@@ -51,7 +51,8 @@ def resample_ohlc(df: pd.DataFrame, rule: str) -> pd.DataFrame:
         {"open": "first", "high": "max", "low": "min", "close": "last", "volume": "sum"})
     out = out.dropna(subset=["open"])
     out["datetime"] = out.index
-    out["timestamp"] = (out.index.view("int64") // 1_000_000)
+    epoch = pd.Timestamp("1970-01-01", tz="UTC")
+    out["timestamp"] = ((out.index - epoch) // pd.Timedelta(milliseconds=1)).astype("int64")
     return out.reset_index(drop=True)[["timestamp", "open", "high", "low", "close", "volume", "datetime"]]