Since the ranges of `unsigned long long` and `long long` are different, we cannot read an
`unsigned long long` integer from a `RedisModuleString` by `RedisModule_StringToLongLong` .
So I added two new Redis Module APIs to support the conversion between these two types:
* `RedisModule_StringToULongLong`
* `RedisModule_CreateStringFromULongLong`
Signed-off-by: RinChanNOWWW <hzy427@gmail.com>