BUG: fixing total_seconds for timedeltas smaller then 1 microsecond

Author: deponovo

pandas/_libs/tslibs/conversion.pyx

@@ -504,7 +504,7 @@ cdef _TSObject convert_datetime_to_tsobject(datetime ts, tzinfo tz,
 
     if obj.tzinfo is not None and not is_utc(obj.tzinfo):
         offset = get_utcoffset(obj.tzinfo, ts)
-        obj.value -= int(offset.total_seconds() * 1e9)
+        obj.value -= int(offset.total_seconds() * 1_000_000_000)
 
     if isinstance(ts, ABCTimestamp):
         obj.value += <int64_t>ts.nanosecond

pandas/_libs/tslibs/timedeltas.pyx

@@ -1520,6 +1520,10 @@ class Timedelta(_Timedelta):
         div = other // self
         return div, other - div * self
 
+    def total_seconds(self):
+        """Total seconds in the duration."""
+        return self.value / 1_000_000_000
+
 
 cdef bint is_any_td_scalar(object obj):
     """