[Python] Cannot mix struct and non-struct, non-null values error when saving nested types with PyArrow

When trying to save a Pandas dataframe with a nested type (list within list, list within dict) using pyarrow engine, the following error is encountered

ArrowInvalid: ('cannot mix list and non-list, non-null values', 'Conversion failed for column A with type object')

Repro:
```java

import pandas as pd
x = pd.DataFrame({"A": [[24, 27, [1, 1]]]})
x.to_parquet('/tmp/a.pqt', engine="pyarrow") 
```
Doing a bit of googling, it appears that this is a known Arrow shortcoming. However, this is a commonly encountered datastructure, and 'fastparquet' handles this seamlessly. Is there a proposed timeline/plan for fixing this?

**Reporter**: [Karthik](https://issues.apache.org/jira/browse/ARROW-15142)

_{**Note**: *This issue was originally created as [ARROW-15142](https://issues.apache.org/jira/browse/ARROW-15142). Please see the [migration documentation](https://github.com/apache/arrow/issues/14542) for further details.*}

Start by reproducing the Pandas DataFrame example with the pyarrow engine and compare its behavior with fastparquet. Trace how the nested values in column A are converted, then add coverage for mixed list and non-list values and confirm that saving the dataframe succeeds.

Written by the indexing model from the issue text.