BUG: Timedelta.total_seconds() precision issue
- [x] closes #19458
- [ ] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19477?src=pr&el=h1) Report
> Merging [#19477](https://codecov.io/gh/pandas-dev/pandas/pull/19477?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/de39a1572fcf82071f3c0b5f22be1611222bdf41?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/19477/graphs/tree.svg?width=650&src=pr&token=eZ4WkYLtcO&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/19477?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #19477   +/-   ##
=======================================
  Coverage   91.62%   91.62%           
=======================================
  Files         150      150           
  Lines       48714    48714           
=======================================
  Hits        44633    44633           
  Misses       4081     4081
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.99% <ø> (ø)` | :arrow_up: |
| #single | `41.75% <ø> (ø)` | :arrow_up: |


------

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> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19477?src=pr&el=footer). Last update [de39a15...b3416b1](https://codecov.io/gh/pandas-dev/pandas/pull/19477?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Thanks! Could you add a test for this, maybe in `pandas/tests/scalar/test_timedelta.py` and a release note? @TomAugspurger okay. I will try to work on tests. What does a release note mean? A line in `doc/source/whatsnew/v0.23.0.txt`: http://pandas.pydata.org/pandas-docs/stable/contributing.html#documenting-your-code ```
rng = Timedelta('30S')
expt = 30.0
tm.assert_almost_equal(rng.total_seconds(), expt)

```
I wrote something like this. Is this correct? you could do
``assert expected - result < 1e-20` can you add a test & a whatsnew note nvm. this was closed via https://github.com/pandas-dev/pandas/pull/19783/files