Arvados

If the new config option (Containers.UseBuiltinMountWhenReadOnly, default false) is true and there will be no writes to the fuse mount (e.g., singularity image cache, output or other writable collection mounts specified by the container), crunch-run should start a Go fuse process instead of arv-mount.

The fuse driver should be started in a separate process via "/proc/self/exe mount ..." or similar, so it works (and uses the same code version as crunch-run itself) without any extra compute worker image preparation. Document any new runtime dependencies (hopefully none -- arv-mount already requires libfuse).

Any missing features, performance regressions, or user-observable differences (e.g., crunchstat) relative to the arv-mount setup should be noted as follow-up issues, but should not be considered blockers. The goal here is to make it possible to enable the Go option, starting with dev clusters, and test/measure for such differences and prioritize them accordingly.