[Python] Nullability not maintained when casting a column

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

Given the following Parquet file:
```
➜ arrow git:(arrow-14705) ✗ parquet-tools inspect ~/Desktop/int.parquet

############ file meta data ############
created_by: parquet-cpp-arrow version 12.0.0
num_columns: 1
num_rows: 3
num_row_groups: 1
format_version: 2.6
serialized_size: 798

############ Columns ############
id

############ Column(id) ############
name: id
path: id
max_definition_level: 0
max_repetition_level: 0
physical_type: INT32
logical_type: None
converted_type (legacy): NONE
compression: SNAPPY (space_saved: -5%)
```

When I widen a type, I see that the not-null is dropped from the schema:


I think this should be maintained.

### Component(s)

Python