Hide internal fields to improve type safety and provide helper methods for unit conversions and negative value checks. Fix several feature-gated test compilation issues.
Simplify RttSample by merging signed and unsigned fields into a single SignedDuration for adjusted and effective RTT. This ensures accurate reporting and statistics when server processing time exceeds raw RTT.
Rename system_time_ns to unix_time_ns_after_epoch for better clarity on output behavior and update a continuous mode test case name to more accurately reflect its purpose.
Nils Andreas Svee