Close `Lighthouse` properly in examples

[fwcd]

We should use the recently added Lighthouse::close method¹ in the examples to avoid closing the WebSocket without sending the close handshake (while not critical, it seems to be good practice to do so):

lighthouse-rust/lighthouse-client/src/lighthouse.rs

Lines 303 to 308 in 87d7b14

	/// Closes the WebSocket connection gracefully with a close message. While
	/// the server will usually also handle abruptly closed connections
	/// properly, it is recommended to always close the [``Lighthouse``].
	pub async fn close(&mut self) -> Result<()> {
	Ok(self.ws_sink.close().await?)
	}

Depending on the type of application, there seem to be two reasonable approaches here:

• For one-shot scripts (e.g. examples/black.rs), simply call (and await) .close() at the end of the script
• For REPLs (e.g. limo) we could likely do the same, but would make sure that ctrl-d properly goes down this code path
• For continuously running applications (e.g. games), set up a signal handler (e.g. await Tokio's ctrl-c) and then call .close()

Footnotes

1. Unfortunately we cannot just put this method into a Drop implementation due to being async and error-throwing. We could look into spawning a task in the drop handler, but that would no longer let us await the close, which could lead to subtle/hard-to-debug race conditions. ↩