docs: def register(self, collector):
          """Add a collector to the registry."""
          with self._lock:
              names = self._get_names(collector)
              duplicates = set(self._names_to_collectors).intersection(names)
              if duplicates:
                  raise ValueError(
                      'Duplicated timeseries in CollectorRegistry: {0}'.format(
                          duplicates))
              for name in names:
                  self._names_to_collectors[name] = collector
              self._collector_to_names[collector] = names