Instead of running `rustup` on a multi-gigabyte general-purpose Linux base, use the premade devcontainers/rust:1 which closely tracks the rust toolchain releases. Rip out excess setup steps since devcontainers come with the repo checked out; just compile/update the binary.
Theses settings files are the base needed to declare and
bootstrap development environment on codespaces
Signed-off-by: Emmanuel Roullit <emmanuel.roullit@gmail.com>
