refactor(client): move internal client tests to a dedicated sub-module

crates/irtt-client/src/client/tests/mod.rs

@@ -0,0 +1,13 @@
+use super::*;
+use crate::config::{NegotiationPolicy, DEFAULT_OPEN_TIMEOUTS};
+use irtt_proto::{
+    echo_packet_len, flags::FLAG_HMAC, flags::FLAG_OPEN, flags::FLAG_REPLY, verify_hmac, Clock,
+    ReceivedStats, StampAt, HMAC_SIZE, MAGIC,
+};
+use std::{thread, time::SystemTime};
+
+mod support;
+use support::*;
+
+mod config_open;
+mod probes_replies;