fix(types): update OHLCV timestamp comment to seconds

Changed the timestamp comment in OHLCV to clarify it uses seconds
instead of milliseconds.

Author: wallneradam

src/pynecore/types/ohlcv.py

@@ -3,7 +3,7 @@
 
 
 class OHLCV(NamedTuple):
-    timestamp: int  # Unix timestamp in milliseconds
+    timestamp: int  # Unix timestamp in seconds
     open: float | NA[float]
     high: float | NA[float]
     low: float | NA[float]