tests: rework the actually useful tests to live in the integration crate

crates/irtt-client/tests/client.rs

@@ -0,0 +1,8 @@
+use irtt_client::*;
+use std::{
+    net::SocketAddr,
+    time::{Duration, Instant},
+};
+
+#[path = "client/mod.rs"]
+mod client;