Add #![no_std] to the runtime crate and introduce optional std and
alloc features. Update the code generator to be compatible and add a
no_std_test example. Remove the generator binary.
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.