Investigate uint64 hash function replacement

Most of the data in configuration cache is indexed by their 64 bit unsigned integer identifiers and uses the same generic hash function that is used for other data. During processing Zabbix spends considerable cpu time (it was around 22% few years ago in poller performance tests) calculating hash sums for 64 bit integers. So finding more efficient hash function would save some processing time (especially when configuration cache lookups must be done while configuration cache is locked).