REGR: window ewm slowdown
- [x] closes #42333
- [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 (will move once 1.3.3 notes merged)

```
-     3.22±0.09ms       1.29±0.3ms     0.40  rolling.EWMMethods.time_ewm('DataFrame', 10, 'int', 'mean')
-      2.92±0.1ms       1.08±0.1ms     0.37  rolling.EWMMethods.time_ewm('DataFrame', 1000, 'int', 'mean')
-      2.68±0.1ms        959±100μs     0.36  rolling.EWMMethods.time_ewm('DataFrame', 1000, 'float', 'mean')
-      3.00±0.2ms      1.02±0.03ms     0.34  rolling.EWMMethods.time_ewm('DataFrame', 10, 'float', 'mean')
-      2.78±0.1ms        850±100μs     0.31  rolling.EWMMethods.time_ewm('Series', 10, 'int', 'mean')
-      2.34±0.2ms         683±30μs     0.29  rolling.EWMMethods.time_ewm('Series', 10, 'float', 'mean')
-     2.74±0.06ms         739±60μs     0.27  rolling.EWMMethods.time_ewm('Series', 1000, 'float', 'mean')
-      2.55±0.3ms         681±40μs     0.27  rolling.EWMMethods.time_ewm('Series', 1000, 'int', 'mean')
```