refactor: remove logical_seq from client events, session tracking and stats usage

It was an attempt at handling integer wraparound more cleanly keeping in mind that we have a continuous mode,
and so we can more easily reach seq > u32::MAX

However after running the numbers, if we run with a interval of 10ms, it's still gonna take ~497 days before we hit integer overflow, so for now it doesn't seem worth to have this extra logic to handle something that'll in 99.9% of cases be purely an edge case

Keeping in mind autorate usage, in sqm-autorate-rust each send loop is 500 ms by default, and the sleep is then 500 ms / 5 reflectors, so our interval is 100 ms. that means it'll take 4970 days or ~13.6 years to reach the limit. Not worth dealing with IMO

crates/irtt-client/src/managed/runner.rs

@@ -594,19 +594,13 @@ mod tests {
         server.join();
 
         assert_eq!(outcome.end_reason, SessionEndReason::TestComplete);
-        assert!(events.iter().any(|event| matches!(
-            event,
-            ClientEvent::EchoLoss {
-                seq: 0,
-                logical_seq: 0,
-                ..
-            }
-        )));
+        assert!(events
+            .iter()
+            .any(|event| matches!(event, ClientEvent::EchoLoss { seq: 0, .. })));
         assert!(events.iter().any(|event| matches!(
             event,
             ClientEvent::LateReply {
                 seq: 0,
-                logical_seq: Some(0),
                 sent_at: Some(_),
                 rtt: Some(_),
                 ..