Add test for torchax_wrapper.py

[lsy323]

Description

Add test for torchax_wrapper.py

The kernel wrapper is not added, I plan to clean up the kernel wrapper since we may handle them cleaner.

Tests

pytest tests/models/vllm/test_torchax_wrapper.py --cov tpu_commons --cov-report term-missing

coverage for torchax_wrapper.py is 73%

Checklist

Before submitting this PR, please make sure (put X in square brackets):

• I have performed a self-review of my code.
• I have necessary comments in my code, particularly in hard-to-understand areas.
• I have made or will make corresponding changes to any relevant documentation.