tests: add end-to-end integration suite (spawns the binary on ephemeral ports; kills by PID, never by name) covering reactor-pool cross-worker delivery, TLS-in-reactor handshake + cross-transport + secure marker, stalled-handshake reap, and nick collision

Cargo.toml

@@ -23,5 +23,9 @@ openssl = "0.10"
 # so the daemon is still `#![forbid(unsafe_code)]`; no async runtime is pulled in.
 mio = { version = "1", features = ["os-poll", "net"] }
 
+[dev-dependencies]
+# integration tests spawn the built binary and act as a TLS client against it
+openssl = "0.10"
+
 [profile.release]
 opt-level = 3