🐛 Overriding a DO's method prevents it being called via RPC

repro: https://github.com/threepointone/override-do-rpc-method

The setup: A Durable Object class that has a method that is overridden inside its constructor.

```ts
class MyDO extends DurableObject {
constructor(state: DurableObjectState, env: Env) {
super(state, env);

const _something = this.something.bind(this);
this.something = (message: string) => {
console.log("overriding something");
return _something(message);
};
}
async something(message: string) {
return `asked ${message}: hello world`;
}
}
```

Nothing fancy, we see that `::something()` is overridden inside its constructor.

Let's call it from a worker:

```ts
export default {
async fetch(_request: Request, env: Env, _ctx: ExecutionContext) {
const id = env.MyDO.idFromName("my-durable-object");
const myDO = env.MyDO.get(id);
const res = await myDO.something("anyone there?");
return new Response(res);
},
};
```

Without the override, we get the expected response: `asked anyone there?: hello world`.

However, with the override, the request doesn't reach the Durable Object, and we get this error:

`The RPC receiver does not implement the method "something".`