runtime, macros: unify NaN-boxed value API under ValueVariant trait

fix-vm/src/instructions/with_scope.rs

@@ -13,7 +13,7 @@ pub(crate) fn op_lookup_with<'gc, M: Machine<'gc>>(
     mc: &gc_arena::Mutation<'gc>,
 ) -> Step {
     #[allow(clippy::unwrap_used)]
-    let counter = m.peek_forced(0).as_inline::<i32>().unwrap();
+    let counter = m.peek_forced(0).downcast::<i32>().unwrap();
 
     let name = reader.read_string_id();
     let n = reader.read_u8();
@@ -57,7 +57,7 @@ pub(crate) fn op_lookup_with<'gc, M: Machine<'gc>>(
     };
 
     if let Some(val) = namespace
-        .as_gc::<AttrSet>()
+        .downcast::<AttrSet>()
         .and_then(|attrs| attrs.lookup(name))
     {
         m.replace(0, val);
@@ -67,7 +67,7 @@ pub(crate) fn op_lookup_with<'gc, M: Machine<'gc>>(
             Symbol::from(ctx.resolve_string(name))
         )));
     } else {
-        m.replace(0, Value::new_inline(counter + 1));
+        m.replace(0, Value::new(counter + 1));
         reader.set_pc(resume_pc);
     }