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.

crates/wraith-core/Cargo.toml

@@ -9,7 +9,7 @@ name = "wraith_core"
 [features]
 default = []
 tls = ["dep:tokio-rustls", "dep:rustls"]
-iroh = ["dep:iroh"]
+iroh = ["dep:iroh", "dep:url"]
 acme = ["dep:rustls-acme", "tls"]
 testutil = []
 transport-traits = []
@@ -25,8 +25,10 @@ tokio-rustls = { version = "0.26", optional = true }
 rustls = { version = "0.23", optional = true }
 rustls-acme = { version = "0.12", optional = true }
 iroh = { version = "0.34", optional = true }
+url = { version = "2", optional = true }
 async-trait = "0.1"
 
 [dev-dependencies]
-wraith-core = { path = ".", features = ["testutil"] }
-tempfile = "3"
+wraith-core = { path = ".", features = ["testutil", "iroh"] }
+tempfile = "3"
+rand = "0.8"