PERF: to_datetime with uint
- [x] closes #42606
- [x] tests added / passed
- [x] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing.html#code-standards) for how to run them
- [x] whatsnew entry

```python
#PR
In [3]: %time index = pd.to_datetime(np.arange(1_000_000).astype("uint64"), unit="s", utc=True)
CPU times: user 20.6 ms, sys: 19.9 ms, total: 40.5 ms
Wall time: 39.2 ms

In [4]: %time index = pd.to_datetime(np.arange(1_000_000).astype("uint32"), unit="s", utc=True)
CPU times: user 16.3 ms, sys: 6.58 ms, total: 22.8 ms
Wall time: 21.2 ms

#master
In [3]: %time index = pd.to_datetime(np.arange(1_000_000).astype("uint64"), unit="s", utc=True)
CPU times: user 12.6 s, sys: 44.3 ms, total: 12.7 s
Wall time: 12.7 s

In [4]: %time index = pd.to_datetime(np.arange(1_000_000).astype("uint32"), unit="s", utc=True)
CPU times: user 5.88 s, sys: 21.2 ms, total: 5.9 s
Wall time: 5.92 s
```