Don't warn if variables produced by the code generator end up unused

sigma-compiler-core/src/codegen.rs

@@ -569,6 +569,7 @@ impl CodeGen {
         };
         quote! {
             #[allow(non_snake_case)]
+            #[allow(unused_variables)]
             pub mod #proto_name {
                 use super::sigma_compiler;
                 use sigma_compiler::group::Group;