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

[schaefer01]

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
#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<r: int16, i: int16> to uint8 using function cast_uint8

Component(s)

Python