refactor(irtt-client): modularize client components

crates/irtt-client/src/timing.rs

@@ -0,0 +1,16 @@
+use std::time::{Instant, SystemTime};
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct ClientTimestamp {
+    pub wall: SystemTime,
+    pub mono: Instant,
+}
+
+impl ClientTimestamp {
+    pub fn now() -> Self {
+        Self {
+            wall: SystemTime::now(),
+            mono: Instant::now(),
+        }
+    }
+}