migrate from libp2p to iroh

[Evanev7]

Motivation

libp2p is fairly far abstracted from networking hardware. Iroh provides an alternative, and this branch has been my work on a potential future migration. I may revive the attempt at some point, but libp2p is working well at the moment. I think the code quality here is better, as is the lack of the nightly rust toolchain, but it doesn't solve any problems we are facing right now.

Changes

Removed our libp2p dependency, removed our rust-nightly dependency, added an iroh-gossip based exo net implementation.

Why It Works

Test Plan

Minimal - basic functionality is there, but little testing.