Update crate references in codegen tests

Update imports to use `roto_tonic` instead of `crate` for BufferPool
and StatusBody. Remove the broad replacement of `crate` with `roto`
and add error output to `test_map_build.rs`.

codegen/tests/build_generated_code.rs

@@ -68,10 +68,11 @@ fn test_generated_code_builds() {
 
     // 4. Write the generated code to src/lib.rs
     // The generated code uses `use crate::{...}`, but it's now in a separate crate.
-    // Replace `crate` with `roto` to reference the types in the dependency.
+    // Replace `crate` with `roto_tonic` to reference the types in the dependency.
     let mut all_code = String::new();
     for (_, content) in generated_files {
-        all_code.push_str(&content);
+        let replaced = content.replace("use crate::{BufferPool, StatusBody};", "use roto_tonic::{BufferPool, StatusBody};");
+        all_code.push_str(&replaced);
         all_code.push_str("\n");
     }
     let lib_path = temp_project_dir.join("src/lib.rs");