Add V3 protocol test suite

[sleeyax]

Would it be possible to add a test-suite for the V3 protocol? I'm adding support for the V3 protocol to socketioxide (an implementation in Rust) and it would definitely help to test the correctness of the implementation without too much guesswork or possible oversight.

[darrachequesne]

Sure, I'll add a test suite for v3 👍

[sleeyax]

If no one has started working on this issue yet, I'd be willing to bootstrap a basic test suite for engine.io V3 protocol and create a PR. It might not cover everything yet as I'm quite new to the protocol and wasn't involved in prior development myself. But it's a start.