Investigate Helion for kernel authoring/tuning

### 🚀 The feature, motivation and pitch

## Summary

[Helion](https://github.com/pytorch/helion) is PyTorch's new DSL that compiles to Triton and has powerful autotuning capabilities. It could make Liger kernels easier to write and more optimized across GPU architectures/problem sizes.

We could tune for some common architectures (e.g. H100/B200) and fallback to some sensible defaults otherwise.

## Potential risks or issues

- Helion is experimental (bugs, API changes)
- Requires additional dependency from users, torch 2.9
- Requires pre-tuning kernels across multiple architectures and shipping several configs, as tuning can take a long time (~10 min)

### Alternatives

_No response_

### Additional context

_No response_

Start by reviewing the current Liger kernel authoring and tuning approach, then evaluate Helion's compatibility, dependency requirements, and support for H100/B200 and fallback configurations. Define the scope and acceptance criteria for any adoption before investigating implementation details; the issue currently names no files or tests.

Written by the indexing model from the issue text.