Return multiple snippets from `format_fn` (separate decl + def).

PiperOrigin-RevId: 508783976
diff --git a/cc_bindings_from_rs/cc_bindings_from_rs.rs b/cc_bindings_from_rs/cc_bindings_from_rs.rs
index 7d643b4..3027780 100644
--- a/cc_bindings_from_rs/cc_bindings_from_rs.rs
+++ b/cc_bindings_from_rs/cc_bindings_from_rs.rs
@@ -288,14 +288,15 @@
 #pragma once
 
 namespace test_crate {
-namespace public_module {
+namespace public_module {"#,
+ // TODO(b/261185414): Avoid assuming that all source code paths are google3 paths.
+format!("// Generated from: google3{temp_dir_str}/test_crate.rs;l=2"),
+r#"inline void public_function();
 namespace __crubit_internal {
 extern "C" void
 __crubit_thunk__ANY_IDENTIFIER_CHARACTERS();
-}"#,
- // TODO(b/261185414): Avoid assuming that all source code paths are google3 paths.
-format!("// Generated from: google3{temp_dir_str}/test_crate.rs;l=2"),
-r#"inline void public_function() {
+}
+inline void public_function() {
   return __crubit_internal::
       __crubit_thunk__ANY_IDENTIFIER_CHARACTERS();
 }