BUG: Timedelta drops decimals if precision is greater than nanoseconds
- [x] closes #36738
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

I am not quite sure, if we should round to nanoseconds or cut if off after the 9th decimal. I implemented a simple cut off, but would be happy to change if rounding is better.

I would also add a note to the user guide if the future behavior is clear
/azp run <samp>
Commenter does not have sufficient privileges for PR 36771 in repo pandas-dev/pandas<br>

</samp> Failure seems weird, maybe rerunning the pipeline? I think truncation is reasonable. I think it would be good to document this behavior in `Timedelta` and `to_timedelta`.

Could you also add a test that goes through `to_timedelta`? The test ran through ``to_timedelta`` but not through ``Timedelta``. Added this one. Also added a note to the docstrings Failure unrelated This pull request is stale because it has been open for thirty days with no activity. Please update or respond to this comment if you're still interested in working on this. Mind merge master @phofl? This LGTM after that  @mroeschke done ci failure is from master and will be fixed with #37756 @phofl I merged that PR, so you can update here as well now Thanks, done thanks @phofl 