@Override
  public String toString() {
    return "CollectorSampler(" + boundary() + ")";
  }
Returns true if spans with this trace ID should be recorded to storage.

<p>Zipkin v1 allows storage-layer sampling, which can help prevent spikes in traffic from
overloading the system. Debug spans are always stored.

<p>This uses only the lower 64 bits of the trace ID as instrumentation still send mixed trace
ID width.

@param hexTraceId the lower 64 bits of the span's trace ID are checked against the boundary
@param debug when true, always passes sampling
zipkin-collector/core/src/main/java/zipkin2/collector/CollectorSampler.java