Handle unions with typing.Callable aliases without TypeError

[Copilot]

Pytest on RustPython failed when evaluating bool | Callable[...] because typing’s _CallableGenericAlias wasn’t accepted as unionable.

• Unionability fix
  • Treat typing generic aliases (objects with __origin__/__args__ from the typing module) as valid union operands alongside built-in types and GenericAlias.
• Regression coverage
  • Added snippet typing_callable_union.py to ensure bool | typing.Callable[[int], int] no longer raises.

Example:

from typing import Callable
TracebackFilter = bool | Callable[[int], int]  # now succeeds

Original prompt

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This section details on the original issue you should resolve

<issue_title>TypeError: '|' not supported between instances of 'type' and '_CallableGenericAlias'</issue_title>
<issue_description>I'm trying to use pytest to have full test coverage in xonsh shell

rustpython -V
# Python 3.13.0alpha (heads/master:40acd5529
rustpython -m pip install pytest
cd /tmp
git clone https://github.com/xonsh/xonsh
cd xonsh
pytest

Traceback (most recent call last):
  File "/Users/pc/.local/bin/pytest", line 3, in <module>
    from pytest import console_main
  File "/Users/pc/.local/lib/rustpython3.13/site-packages/pytest/__init__.py", line 8, in <module>
    from _pytest._code import ExceptionInfo
  File "/Users/pc/.local/lib/rustpython3.13/site-packages/_pytest/_code/__init__.py", line 5, in <module>
    from .code import Code
  File "/Users/pc/.local/lib/rustpython3.13/site-packages/_pytest/_code/code.py", line 862, in <module>
    TracebackFilter: TypeAlias = bool | Callable[[ExceptionInfo[BaseException]], Traceback]
TypeError: '|' not supported between instances of 'type' and '_CallableGenericAlias'
```</issue_description>

## Comments on the Issue (you are @copilot in this section)

<comments>
</comments>

• Fixes TypeError: '|' not supported between instances of 'type' and '_CallableGenericAlias' #6538

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[github-actions]

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git pull origin copilot/fix-typeerror-in-pytest