[Python] cast doesn't work for structure in pyarrow

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

these are the links for the C++ issue that was solved and closed.

https://issues.apache.org/jira/browse/ARROW-1888
https://github.com/apache/arrow/issues/17882

please do the same for python:

>> import pyarrow as pa
>> pa.__version__
'12.0.0

>> pa_bytes = pa_result.cast(target_type=pa.uint8())
Traceback (most recent call last):
File "", line 1, in
File "pyarrow/array.pxi", line 935, in pyarrow.lib.Array.cast
File "/usr/local/lib/python3.8/site-packages/pyarrow/compute.py", line 400, in cast
return call_function("cast", [arr], options, memory_pool)
File "pyarrow/_compute.pyx", line 572, in pyarrow._compute.call_function
File "pyarrow/_compute.pyx", line 367, in pyarrow._compute.Function.call
File "pyarrow/error.pxi", line 144, in pyarrow.lib.pyarrow_internal_check_status
File "pyarrow/error.pxi", line 121, in pyarrow.lib.check_status
pyarrow.lib.ArrowNotImplementedError: Unsupported cast from struct to uint8 using function cast_uint8

### Component(s)

Python

Start at the Python Array.cast entry point in pyarrow/array.pxi and follow the cast path through pyarrow/compute.py and pyarrow/_compute.pyx. Compare the behavior with ARROW-1888 and GitHub issue 17882, then verify that the reproduced struct to uint8 cast no longer raises ArrowNotImplementedError.

Written by the indexing model from the issue text.