The host-executor runners run jobs inside one container that already has
the Rust toolchain and all build dependencies baked in, so the per-job
`apt-get install` and rustup steps were redundant. Worse, with two jobs
running concurrently in the same runner they collided on the dpkg lock
("Could not get lock /var/lib/dpkg/lock-frontend").
Remove the system-dependency, rustup and cache steps; jobs now run cargo
directly. The cargo registry persists in the long-lived runner container.
Assisted-By: Claude Code (claude-opus-4)
Claude-Session: https://claude.ai/code/session_01NFpGtGTWUEYXLwZeZs2RAV
Signed-off-by: Stan Grams <sjg@haxx.space>