Apply additional lints suggested by cargo clippy

rust/ares/src/hamt.rs

@@ -428,6 +428,12 @@ impl<T: Copy> Hamt<T> {
     }
 }
 
+impl<T: Copy> Default for Hamt<T> {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 impl<T: Copy + Preserve> Preserve for Hamt<T> {
     unsafe fn preserve(&mut self, stack: &mut NockStack) {
         if stack.in_frame(self.0.buffer) {

rust/ares/src/newt.rs

@@ -218,3 +218,9 @@ impl Newt {
         Some(cue(stack, atom))
     }
 }
+
+impl Default for Newt {
+    fn default() -> Self {
+        Self::new()
+    }
+}

rust/ares/src/noun.rs

@@ -370,7 +370,7 @@ impl IndirectAtom {
             if index == 0 || *(data.add(index)) != 0 {
                 break;
             }
-            index = index - 1;
+            index -= 1;
         }
         *(self.to_raw_pointer_mut().add(1)) = (index + 1) as u64;
         self