Hole punching implementation and improvements to networking including Steam P2P

[diamondpixel]

Note: This PR is a bit out of scope, but it introduces lobbies support, including Steam Lobbies and several Steam-related
improvements (still a work in progress).

It also adds proper resource cleanup when leaving a lobby and starting a new one, preventing leftover state and leaks.

I have an additional PR prepared that focuses on packet allocation optimization, bringing allocations close to zero. In testing,
this resulted in roughly 600 MB lower memory usage and much more consistent CPU usage.

[diamondpixel]

By the way i may and may not, have included my Public IP accidentally on the commit.....

[Extremelyd1]

I've finished the review, there are a couple of comments left that I would like to see changed and one somewhat larger question about whether we need to contact an external STUN server.
Apart from that the code looks pretty good. I'll save functional testing until this branch is ready to be merged with main. We need to keep in mind to change the hostname (and maybe port) of the MMS when we do.

[Extremelyd1]

A couple instances of Buffer.BlockCopy instead of Array.Copy and a single comment still. I've commited some style, comment, and compiler warning supression fixes already.

[Extremelyd1]

I missed this in earlier reviews, but you shouldn't have made the return type nullable here. The method either finds the packet data or creates a new instance of it. So in all cases the method returns a non-null instance of packet data.