public int threads() {
    String value = getArg("threads", Integer.toString(Runtime.getRuntime().availableProcessors()));
    int threads = Math.max(2, Integer.parseInt(value));
    logArgValue("threads", "num threads", threads);
    return threads;
  }
Returns the number of threads from {@link Runtime#availableProcessors()} but allow the user to override it by
setting the {@code threads} argument.

@throws NumberFormatException if {@code threads} can't be parsed as an integer
planetiler-core/src/main/java/com/onthegomap/planetiler/config/Arguments.java