fix(websocket): polyfill missing ErrorEvent global

[otnc]

Node.js has no global ErrorEvent (unlike Event, MessageEvent, and CloseEvent,
which are already polyfilled/native). When the underlying ws socket emits an
error event, upgradeWebSocket's handler does new ErrorEvent('error', { error }),
which throws a ReferenceError on every supported Node version. That error is caught
and passed to the internal onError fallback instead — so the user's onError
handler passed to upgradeWebSocket is never invoked, and the original error is lost.

This adds an ErrorEvent polyfill following the same pattern as the existing
CloseEvent one, and adds a test that reproduces the bug by emitting a real
error event on the raw socket and asserting the user's onError receives it.

[yusukebe]

LGTM!

[yusukebe]

@otnc

Good catch! Looks good. Thank you!