clippy: Enable `non_canonical_partial_ord_impl` rule

Cargo.toml

@@ -172,7 +172,6 @@ borrowed_box = "allow"
 derived_hash_with_manual_eq = "allow"
 forget_non_drop = "allow"
 needless_doctest_main = "allow"
-non_canonical_partial_ord_impl = "allow"
 too_many_arguments = "allow"
 type_complexity = "allow"
 wrong_self_convention = "allow"

lib/la-arena/src/lib.rs

@@ -70,7 +70,7 @@ impl<T> Ord for Idx<T> {
 
 impl<T> PartialOrd for Idx<T> {
     fn partial_cmp(&self, other: &Self) -> Option<cmp::Ordering> {
-        self.raw.partial_cmp(&other.raw)
+        Some(self.cmp(other))
     }
 }