PERF: ArrowExtensionArray.__iter__
- [x] [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.

Faster iteration through pyarrow-backed arrays.

```
from asv_bench.benchmarks.strings import Iter

dtype = "string[pyarrow]"
bench = Iter()
bench.setup(dtype)

%timeit bench.time_iter(dtype)

# 266 ms ± 6.66 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)    <- main
# 57.7 ms ± 679 µs per loop (mean ± std. dev. of 7 runs, 10 loops each)  <- PR
```
Thanks @lukemanley! 