feat!: introduce iroh-router crate (#2832)

The general goal is to have a single place to deal with custom
protocols.

## Breaking Changes

- moved
  - `iroh::node::ProtocolHandler` -> `iroh::router::ProtocolHandler`

---------

Co-authored-by: Floris Bruynooghe <flub@n0.computer>

Cargo.toml

@@ -8,6 +8,7 @@ members = [
   "iroh-test",
   "iroh-net/bench",
   "iroh-cli",
+  "iroh-router",
 ]
 resolver = "2"
 
@@ -49,3 +50,4 @@ iroh-base = { path = "./iroh-base" }
 iroh-net = { path = "./iroh-net" }
 iroh-metrics = { path = "./iroh-metrics" }
 iroh-test = { path = "./iroh-test" }
+iroh-router = { path = "./iroh-router" }