Change StatusBody from a tuple struct to a struct containing both data
and trailers. Update the codegen to use the new StatusBody::new
constructor to specify gRPC status codes.
Also remove the temp_test_project.
Resolve `Result` ambiguity and lifetime issues in generated services.
Use `file_stem` for proto filenames. Make `StatusBody` public in
`roto-tonic` and update the `hello_world` build process.
charles