Fix code generator and add compilation test

Correct module paths and accessor usage in the generator to ensure
generated code builds. Add a test that verifies this by compiling the
generated code in a temporary project.

Cargo.lock

@@ -1352,6 +1352,23 @@ version = "1.0.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "0bf256ce5efdfa370213c1dabab5935a12e49f2c58d15e9eac2870d3b4f27263"
 
+[[package]]
+name = "temp_test_project"
+version = "0.1.0"
+dependencies = [
+ "bytes",
+ "futures-util",
+ "http",
+ "http-body",
+ "http-body-util",
+ "roto-codegen",
+ "roto-runtime",
+ "roto-tonic",
+ "tokio-stream",
+ "tonic",
+ "tower 0.4.13",
+]
+
 [[package]]
 name = "tempfile"
 version = "3.27.0"