Cas Tfr Sources

cas — OpenTofu/Terraform registry sources

Module sources of the form tfr://... are now content-addressed in CAS. Repeat runs against the same pinned registry version reuse the cached module instead of re-downloading the archive from the registry.

CAS resolves a tfr:// source by asking the registry where the underlying archive lives and uses that resolved URL as the cache key. Two runs that pin the same version share one entry; a republish under the same version pins to a new entry, so a stale cache cannot serve outdated bytes.