fix: avoid out-of-range nanoseconds field in pandas 1.5.x (#148)

Author: tswast

db_dtypes/__init__.py

@@ -150,7 +150,8 @@ def _datetime(
                 hour=int(hour),
                 minute=int(minute) if minute else 0,
                 second=int(second) if second else 0,
-                nanosecond=nanosecond,
+                microsecond=nanosecond // 1000,
+                nanosecond=nanosecond % 1000,
             ).to_datetime64()
         else:
             raise TypeError("Invalid value type", scalar)