[Python] Schema Field introspection fails on ListType

### Describe the bug, including details regarding any error messages, version, and platform.

Doing introspection on a Schema object fails on ListType fields.
On this example schema:

```python
test_schema = pa.schema([
('f0', pa.string()),
('f1', pa.list_(pa.string())),
])
```

The string representation is:
```
print(test_schema)
f0: string
f1: list
child 0, item: string
```

When doing introspection with the flatten method, it fails to go through the "item" layer of the list, and instead iterates infinitely on it:

```python
print(test_schema.field(1).name)
print(test_schema.field(1).flatten())
print(test_schema.field(1).flatten()[0].flatten())
...
```

```
f1
[pyarrow.Field>]
[pyarrow.Field>]
...
```

I would expect the following result:
```
f1
[pyarrow.Field>]
[pyarrow.Field]
```

That would allow to iterate through the whole schema fields.

### Component(s)

Python