ignore unused_parens warning

parens are generated by external macro

src/arena.rs

@@ -1,4 +1,5 @@
 #![allow(clippy::new_without_default)] // annotating structs annotated with #[bitfield] doesn't work
+#![allow(unused_parens)] // see mthom/scryer-prolog#3092 and rust-lang/rust#147126
 
 #[cfg(feature = "http")]
 use crate::http::{HttpListener, HttpResponse};