Before this change, the following error would be thrown when compiling
with TypeScript:
```
node_modules/engine.io-client/build/esm/transports/websocket.node.d.ts:12:101 - error TS1340: Module 'ws' does not refer to a type, but is used as a type here. Did you mean 'typeof import('ws')'?
12 createSocket(uri: string, protocols: string | string[] | undefined, opts: Record<string, any>): import("ws");
~~~~~~~~~~~~
```
This behavior was introduced in [1], included in version `6.6.0`.
The return type is forced as `any`, so that the `@types/ws` dependency
is optional.
[1]: f4d898ee96
Related: https://github.com/socketio/socket.io/issues/5202
When a laptop is suspended or a phone is locked, the timer that is used
to check the liveness of the connection is paused and is not able to
detect that the heartbeat has failed.
Previously, emitting a message after resuming the page would lose the
message. The status of the timer will now be checked before sending the
message, so that it gets buffered and sent upon reconnection.
Note: we could also have used the Page Visibility API or a custom
setTimeout() method based on setInterval(), but this would not be as
reliable as the current solution.
Reference: https://developer.mozilla.org/en-US/docs/Web/API/Page_Visibility_API
Related: https://github.com/socketio/socket.io/issues/5135
