fn get_docker_image(tag: &str) -> String {
    std::env::var("SP1_DOCKER_IMAGE").unwrap_or_else(|_| {
        let image_base = "ghcr.io/succinctlabs/sp1";
        format!("{}:{}", image_base, tag)
    })
}
Uses SP1_DOCKER_IMAGE environment variable if set, otherwise constructs the image to use based
on the provided tag.
crates/build/src/command/docker.rs