This diff introduces changes to the Buildkite to change the build commands for Tunnelbroker from `cmake` to use `cargo build` and `cargo test` instead. Also, we are removing the `target` directory before building to remove the cache.
Related Linear task: [[ https://linear.app/comm/issue/ENG-2062/make-changes-to-tunnelbroker-ci-nix-to-change-build-system | ENG-2062 ]]