Implement C Level Timedelta ISO Function; fix JSON usage
- [X] closes #28256
- [X] tests added / passed
- [X] passes `black pandas`
- [X] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [X] whatsnew entry

similar to @cbertinato great work in #28595 but done deeper in the C extension
Current benchmarks:

```sh
       before           after         ratio
     [447a3b00]       [4a94f159]
     <master>         <json-timedelta>
+         152±3ms         209±10ms     1.38  io.json.ToJSONISO.time_iso_format('values')
+         168±3ms         213±10ms     1.27  io.json.ToJSONISO.time_iso_format('records')
+         188±4ms         235±10ms     1.25  io.json.ToJSONISO.time_iso_format('split')
+         195±4ms         238±10ms     1.22  io.json.ToJSONISO.time_iso_format('columns')
-        103±10ms         79.2±6ms     0.77  io.json.ToJSON.time_to_json('values', 'df_td_int_ts')
-        137±20ms         95.9±1ms     0.70  io.json.ToJSON.time_to_json('values', 'df_int_float_str')
```

So the time_iso_format checks are taking a little bit longer but note that they were broken before, i.e. on master you get this:

```python
>>> pd.Series([pd.Timedelta(days=1)], index=[pd.Timedelta(days=1)]).to_json(date_format="iso")
'{"P1DT0H0M0S":"1970-01-02T00:00:00.000Z"}'
```
Where we are writing as dates and not durations.

I think just a matter of the timedelta -> iso function not being as fast (using sprintf instead of totally hand-coded) but maybe OK for now pls rebase LGTM cc @jreback needs rebase, other good to go i think completely closes #28256. ?

can you check the perf again. Yea closes; added some more test coverage as well.

Here is an updated benchmark:

```sh
       before           after         ratio
     [402c5cdd]       [ef08ad6c]
     <json-test-cleanup~1^2>       <json-timedelta>
+        143±20ms         225±10ms     1.57  io.json.ToJSONISO.time_iso_format('values')

SOME BENCHMARKS HAVE CHANGED SIGNIFICANTLY.
PERFORMANCE DECREASED.
``` this is slower? Slower but correct > Slower but correct

worth the tradeoff every time. thanks, correct wins every time.