Add download-jax-rocm-wheels composite action
Create GitHub Actions composite action to download JAX and ROCm wheels.
Supports downloading from PyPI (jaxlib and jax-rocm plugins) or GitHub
releases (custom jaxlib with ROCm plugins), with ROCm version mapping
and platform-specific filtering.
Default versions: JAX 0.9.0, ROCm 7.2.0, GitHub release tag rocm-jax-v0.9.0-rc.
Uses gh CLI for GitHub release downloads and pip for PyPI packages.
