BUG: Series(pyarrow-backed).round raising AttributeError
- [ ] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [x] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [x] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
- [x] Added an entry in the latest `doc/source/whatsnew/v2.0.0.rst` file if fixing a bug or adding a new feature.

Adding `ArrowExtensionArray.round` to fix the following:

```
import pandas as pd

pd.Series([1.23], dtype="float64[pyarrow]").round(1)

# AttributeError: 'ArrowExtensionArray' object has no attribute 'round'
```
Thanks @lukemanley 