Remove alloc guards and update codegen

Remove unnecessary `alloc` feature guards in `roto-tonic`. Add
`roto-runtime` dependency to `codegen`, fix test data paths, and
include `async-trait` in the hello world build test.

codegen/src/runtime/mod.rs

@@ -646,7 +646,7 @@ mod tests {
 
     #[test]
     fn test_protoc_binary_compatibility() {
-        let data = include_bytes!("../data/test_data.pb");
+        let data = include_bytes!("../../data/test_data.pb");
         let acc = ProtoAccessor::new(data).unwrap();
 
         // 1. Varints (Integers, Booleans, Enums)