fix(function): gate test-only declaration appender behind cfg(test)

append_declaration is exercised only by unit tests; in the plain bin
target it tripped dead_code under CI's RUSTFLAGS --deny warnings.

src/function/mod.rs

@@ -693,6 +693,7 @@ impl Functions {
         self.declarations.extend(jobs::job_function_declarations());
     }
 
+    #[cfg(test)]
     pub fn append_declaration(&mut self, declaration: FunctionDeclaration) {
         self.declarations.push(declaration);
     }