feat: gc-arena

finally...

src/ty/internal/mod.rs

@@ -604,13 +604,13 @@ impl<'gc> Thunk<'gc> {
         }
     }
 
-    pub fn suspend(&self, mc: &Mutation<'gc>) -> (&'gc OpCodes, Gc<'gc, VmEnv<'gc>>) {
+    pub fn suspend(&self, mc: &Mutation<'gc>) -> Result<(&'gc OpCodes, Gc<'gc, VmEnv<'gc>>)> {
         let _Thunk::Code(opcodes, env) =
             std::mem::replace(&mut *self.thunk.borrow_mut(mc), _Thunk::Suspended)
         else {
-            unreachable!()
+            return Err(Error::EvalError("infinite recursion occured".into()))
         };
-        (opcodes, env.unwrap())
+        Ok((opcodes, env.unwrap()))
     }
 
     pub fn insert_value(&self, value: Value<'gc>, mc: &Mutation<'gc>) {