Implement IrohTransport and IrohAcceptor (feature-gated iroh)

Add iroh QUIC P2P transport using tokio::io::join for stream duplexing
per ADR-003. Default relay is n0's https://relay.iroh.network/ (ADR-009).
Proxy URL passed to Endpoint::builder (ADR-010). Integration test marked
#[ignore] for CI since it requires iroh relay connectivity.

Cargo.lock

@@ -5476,6 +5476,7 @@ dependencies = [
  "anyhow",
  "async-trait",
  "iroh",
+ "rand 0.8.6",
  "russh",
  "rustls",
  "rustls-acme",
@@ -5485,6 +5486,7 @@ dependencies = [
  "tokio-rustls",
  "tokio-util",
  "tracing",
+ "url",
  "wraith-core",
 ]