feat(http2): add HTTP/2 support

[Abdel-Monaam-Aouini]

This PR adds native HTTP/2 support to Express, allowing developers to leverage HTTP/2's performance improvements while maintaining Express's familiar API.
Features :

1. Complete HTTP/2 integration with both plain and secure (TLS) servers
2. Compatible API with existing Express applications
3. Proper handling of HTTP/2 streams, headers, and request/response objects
4. Comprehensive test suite that verifies all aspects of HTTP/2 functionality
5. Example application demonstrating HTTP/2 usage

[Abdel-Monaam-Aouini]

@wesleytodd any updates here

[bjohansebas]

Thanks for your interest in working on this. I’m helping to lead this together with the whole team. There are a few things I’ve noticed:

• This doesn’t fully test all the properties that Express has — only a few of them.

• This needs to be done through the compatibility layer and ALPN negotiation; it’s more practical, requires less maintenance, and also supports fallback to HTTP/1.1.

  • Technically, to do that we need to stop altering the prototype of ServerResponse and IncomingMessage (see #6669), and we still need to figure out as a team how to achieve that. Ideally, we’d do something similar to how Fastify did it. (That will be done in a separate PR, since it could be a breaking change and requires extensive review to avoid accidentally breaking anything)

• Most importantly, this is not going to be released very soon. We still need to decide as a team what will be included in Express v6, and while this is one of those things, there are other aspects that could affect it. That’s why you haven’t seen comments yet on how to move forward. I hope that doesn’t discourage you — there are many moving parts within Express to make this happen :) so the process is a bit slow. I encourage you to join the other conversations happening around this, because many things are connected to this work.