This supports 128-bit traces via a new field traceIdHigh, which matches other zipkin implementations. In encoded form, the trace ID is simply twice as long (32 hex characters). With this change in, a 128-bit trace propagated will not be downgraded to 64-bits when sending downstream, reporting to Zipkin or adding to the logging context. This will be followed by a change to support initiating 128-bit traces.