ENH: Fix total seconds in timedelta
- [x] closes #40946
- [x] tests added / passed
- [x] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit) for how to run them
- [x] whatsnew entry

As of now, I could not figure out what's leading to test failing in pandas\tests\scalar\timestamp\test_constructors.py:609.
also some tests are failing > also some tests are failing

Yes, I referred that in the entry PR message. I could not figure out what the reason is and I am lacking the time to further seek the source. Maybe somebody already knows the issue or could help? 
The hour difference from a given timezone flips ahead (but short) of the real timestamp flip to the next hour.

cc @mroeschke This comment might potentially be relevant https://github.com/pandas-dev/pandas/pull/31155/files#r370721655 @mroeschke Now back to the original method signature: 
```
    def total_seconds(self):
        """Total seconds in the duration."""
        return self.value / 1_000_000_000
```


This is puzzling. I can't still figure out the source of the prob. I modified the `nanosecond` variable from `_Timestamp` in `pandas/_libs/tslibs/timestamps.pxd` to be public (just for testing purposes) and set it to 0 by default. Then tested a boundary condition:

```
>>> td = pd.Timestamp(1552211999999999999,  tz="dateutil/America/Los_Angeles")
>>> td
Timestamp('2019-03-10 01:59:59.999999-0800', tz='dateutil/US/Pacific')
>>> td.value
1552211999999999999
>>> td.nanosecond
0
>>> td.nanosecond = 999  # actually just assigning the nanosecond part of the original value
>>> td  # note the false -7
Timestamp('2019-03-10 01:59:59.999999999-0700', tz='dateutil/US/Pacific')
>>> td.value
1552211999999999999
>>> td.nanosecond
999
``` > @mroeschke Now back to the original method signature:
> 
> ```
>     def total_seconds(self):
>         """Total seconds in the duration."""
>         return self.value / 1_000_000_000
> ```
> 
> This is puzzling. I can't still figure out the source of the prob. I modified the `nanosecond` variable from `_Timestamp` in `pandas/_libs/tslibs/timestamps.pxd` to be public (just for testing purposes) and set it to 0 by default. Then tested a boundary condition:
> 
> ```
> >>> td = pd.Timestamp(1552211999999999999,  tz="dateutil/America/Los_Angeles")
> >>> td
> Timestamp('2019-03-10 01:59:59.999999-0800', tz='dateutil/US/Pacific')
> >>> td.value
> 1552211999999999999
> >>> td.nanosecond
> 0
> >>> td.nanosecond = 999  # actually just assigning the nanosecond part of the original value
> >>> td  # note the false -7
> Timestamp('2019-03-10 01:59:59.999999999-0700', tz='dateutil/US/Pacific')
> >>> td.value
> 1552211999999999999
> >>> td.nanosecond
> 999
> ```

Looking into https://github.com/pandas-dev/pandas/pull/31155/files#r370721655 might solve this issue This pull request is stale because it has been open for thirty days with no activity. Please [update](https://pandas.pydata.org/pandas-docs/stable/development/contributing.html#updating-your-pull-request) and respond to this comment if you're still interested in working on this. Thanks for the pull request but appears to have gone stale. If you're interested in continuing please merge in main, address the comments and we can reopen.