HyphaeVM Cons instruction prototype

This commit implements the Cons instruction with desired behavior.
Tests are yet to be implemented for any instruction, but are coming
soon.

Signed-off-by: Ava Affine <ava@sunnypup.io>

hyphae/src/heap.rs

@@ -41,7 +41,7 @@ use organelle::Number;
 
 /* Gc
  * This is a heap allocated Rc passed around such that it fits into
- * a physical register. The pointer is to a Box<Rc<T>>, but custom 
+ * a physical register. The pointer is to a Box<Rc<T>>, but custom
  * deref implementation will ensure that deref always points to the
  * encapsulated T
  */
@@ -201,6 +201,22 @@ impl Cons {
 
         1 + next.len()
     }
+
+    pub fn append(&mut self,  arg: Gc<Datum>) {
+        let Some(_) = self.0 else {
+            self.0 = Some(arg);
+            return
+        };
+
+        if let Some(next) = &mut self.1 {
+            if let Datum::Cons(next) = next.deref_mut() {
+               next.append(arg);
+               return;
+            }
+        }
+
+        self.1 = Some(Datum::Cons(Cons(Some(arg), None)).into());
+    }
 }