message: [lang] No longer generate impl block if there are no non-message methods defined
diff: @@ -264,11 +264,13 @@ fn codegen_for_method_impls(tokens: &mut TokenStream2, contract: &hir::Contract)
  }
  content
  };
  + if contract.methods.iter().count() > 0 {
  tokens.extend(quote! {
  impl #state_name {
  #methods_impls
  }
  - });
  + })
  + }
  }
  struct CustomArgCaptured {
  