[Torchax] fp8 quantization skeleton

[xingliu14]

Description

This PR adds the infrastructure skeleton for FP8 quantization support on TPU, following the established pattern from AWQ quantization.

Changes

• Added FP8 constant to quant_methods.py
• Created VllmFp8Config extending Fp8Config and JaxCommonConfig
• Created VllmFp8LinearMethod extending Fp8LinearMethod with skeleton methods
• Registered FP8 in quantization method registry
• Added placeholder test file
• Fixed typo in awq.py comments

Addressing #1121.

Tests

Please describe how you tested this change, and include any instructions and/or
commands to reproduce.

Checklist

Before submitting this PR, please make sure:

• 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.

[xingliu14]

@kyuyeunk PTAL.