Add custom debug impl for obj::int::Int

This removes the vtable and attrs members from appearing, which muddies
up what we really care about with ints

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

src/obj/int.rs

@@ -1,9 +1,10 @@
 use crate::obj::prelude::*;
 use shredder::Scan;
+use std::fmt::{Debug, Formatter, self};
 
 pub type IntRef = ObjRef<Int>;
 
-#[derive(Debug, Scan)]
+#[derive(Scan)]
 pub struct Int {
     value: i64,
     vtable: Vtable,
@@ -28,3 +29,11 @@ impl Int {
 }
 
 impl_obj_readonly!(Int);
+
+impl Debug for Int {
+    fn fmt(&self, fmt: &mut Formatter) -> fmt::Result {
+        fmt.debug_struct("Int")
+            .field("value", &self.value)
+            .finish()
+    }
+}