Lost number precision when saving to redis

Hi!

I've found a vary bad thing... as i have investigated, lua-resty-redis loose 64bit number precision, when saving numbers to redis.

See examples below. Lets assume, we have a number 1824192940134586

REDIS CLI CODE

127.0.0.1:6379[5]> set BIG_NUM_AS_NUM_REDIS 1824192940134586
OK
127.0.0.1:6379[5]> get BIG_NUM_AS_NUM_REDIS
"1824192940134586"

Everything works as expected

Now lets work with number through lua-resty-redis

NGINX LUA CODE

-- first, lets save a number in redis
redis:set("BIG_NUM_AS_NUM", 1824192940134586)
redis:set("BIG_NUM_AS_STR", string.format("%16.0f",1824192940134586))

-- now lets get keys
ngx.log(ngx.ERR, "BIG_NUM_AS_NUM: ", redis:get("BIG_NUM_AS_NUM"))
-- prints: 1.8241929401346e+15
ngx.log(ngx.ERR, "BIG_NUM_AS_NUM(tostr): ", string.format("%16.0f",redis:get("BIG_NUM_AS_NUM")))
-- prints: 1824192940134600 - FAIL
ngx.log(ngx.ERR, "BIG_NUM_AS_STR: ", redis:get("BIG_NUM_AS_STR"))
-- prints: 1824192940134586 - OK

ngx.log(ngx.ERR, "BIG_NUM_AS_NUM_REDIS: ", redis:get("BIG_NUM_AS_NUM_REDIS"))
-- prints: 1824192940134586 - OK
ngx.log(ngx.ERR, "BIG_NUM_AS_NUM_REDIS(tostr): ", string.format("%16.0f",redis:get("BIG_NUM_AS_NUM_REDIS")))
-- prints: 1824192940134586 - OK

Start with the provided Nginx Lua reproduction, especially the redis:set and redis:get calls, and trace how numeric arguments and returned values are represented. Compare the numeric and string examples to determine where precision is lost; done means the reported 1824192940134586 value survives the client round trip without changing.