[pandas] Fix pandas Timedelta total_seconds return type (#169)

The `total_seconds` method returns a float, rather than an int.

This can be tested/confirmed as follows:

```python
import pandas as pd
ptd = pd.to_timedelta(1234.5678, unit="s")
print(ptd.total_seconds())  # 1234.5678
print(type(ptd.total_seconds()))  # <class 'float'>
print(type(ptd))  # <class 'pandas._libs.tslibs.timedeltas.Timedelta'>
```

Author: sjdemartini

partial/pandas/_libs/tslibs/timedeltas.pyi

@@ -77,7 +77,7 @@ class Timedelta(_Timedelta):
     def to_numpy(self) -> _np.timedelta64: ...
     def to_pytimedelta(self) -> datetime.timedelta: ...
     def to_timedelta64(self) -> _np.timedelta64: ...
-    def total_seconds(self) -> int: ...
+    def total_seconds(self) -> float: ...
 
 
 def delta_to_nanoseconds(delta: _Timedelta) -> int: ...