HTTP unmarshal a number into an interface{} as json.Number instead of float64

[aniketnk]

fixes #1163

reference: https://pkg.go.dev/encoding/json#Decoder.UseNumber

UseNumber causes the Decoder to unmarshal a number into an interface{} as a Number instead of as a float64.

Changes

• Use json.Decoder with UseNumber option to unmarshal the JSON object received from http handler.
• Added a testcase for math.MinInt64.
• Added testcases for errors.

Output

SET

curl --location --request GET 'localhost:8082/set' \
--header 'Content-Type: application/json' \
--data '{
    "key" : "a",
    "value" : -9223372036854775808
}'
{"status":"success","data":"OK"}

GET

curl --location --request GET 'localhost:8082/get' \
--header 'Content-Type: application/json' \
--data '{
    "key" : "a"
}'
{"status":"success","data":-9223372036854775808}