public static long getMaxDirId(final Path parentDir) {
        return LOGGER.logDurationIfDebugEnabled(
                () ->
                        getDirIdFromRoot(parentDir, Mode.MAX),
                () ->
                        LogUtil.message("Get max dirId for {}", parentDir));
    }
Get the max id of any numerically named file found in the supplied dir.

@param parentDir The parent dir to look at.
@return The max id of all files found in a dir or 0 if non found.
stroom-state/stroom-planb-impl/src/main/java/stroom/planb/impl/data/DirUtil.java