refactor(client): use SignedDuration for one-way delay to support negative values

Allow one-way delay samples to represent negative values caused by wall-clock skew between client and server. Update CLI output and statistics collection to correctly handle and report these signed durations.

crates/irtt-stats/src/normalization.rs

@@ -163,10 +163,10 @@ impl ReplySample {
             rtt_adjusted_ns: rtt.adjusted.map(signed_duration_ns),
             send_delay_ns: one_way
                 .and_then(|sample| sample.client_to_server)
-                .map(duration_ns_i128),
+                .map(signed_duration_ns),
             receive_delay_ns: one_way
                 .and_then(|sample| sample.server_to_client)
-                .map(duration_ns_i128),
+                .map(signed_duration_ns),
             server_processing_ns: server_timing
                 .and_then(|timing| timing.processing)
                 .map(duration_ns_i128),