Tools for image builds

• proot — is a "Type-0" (or "pure userspace") container runtime… it fakes syscalls in userspace
• charliecloud — is a Type-1/2/3 container runtime
• apptainer — is a Type-2/3 container runtime
• buildah — is a Type-2/3 container runtime for image building
• oras — is a tool to interact with OCI registries (push/pull/delete…)
• skopeo — is a tool for container image conversions and OCI registry interaction