fix(ci): isolate wheel builder storage

[AlpinDale]

Summary

• mount the ROCm rootless BuildKit state directory on its dedicated RAM disk
• target CUDA and ROCm cache pruning at their explicit builders
• preserve compiler cache mounts while pruning disposable layers

Validation

• pre-commit on all changed files
• shell syntax checks
• recreated the runner builder and verified 300 GiB is mounted at /home/user/.local/share/buildkit