Faster disk reads on Scaleway Apple Silicon runners via Tart host-side disk caching

CAPI Scaleway Apple Silicon runners now pass --root-disk-opts caching=cached to tart run for the ephemeral build VMs, so the host page-caches the VM’s sparse disk-image reads instead of falling back to Tart’s automatic policy. On-runner A/B testing on a Scaleway M2-L host measured warm reads climbing from 4.2 GB/s under the default to 7.7 GB/s (~1.8x faster). Because the VMs are cloned per Pod and discarded on exit, the host-side read cache is pure upside with no durability tradeoff. Expect faster builds on the Scaleway CAPI runner fleet as the updated tart-kubelet binary rolls out to each Mac mini host.