fix(ws): calling close event with destroyed close callback

[flisky]

I notice the following error:

And it's 100% reproduced when wasm-pack test --chrome.

It's a racing condition:

• call Websocket::close, which consumes the ownership.
• Websocket::drop is executed emmediately
  • call self.ws.close() the second time (and it doesn't matter).
  • the closures (event listeners) are dropped (and it matters).
• self.ws.onclose is called with destroyed close callback.

Solution:

• bindopen/close event listeners once (which I think okay, tell me if not)
• unbind the open/message/error eventlisteners when dropping
• trigger close event to notify the user (and unbind).

[ranile]

Thanks for the PR! Sorry, took me so long to merge this