Rewrite if operator with while loop

[yichaulin]

Description

#each_slice would cause additional object allocations. Using basic while loop would have better performance.

Performance Benchmark

Test Suit

require 'benchmark/ips'
require "bundler/gem_tasks"
require 'json_logic'

true_case = {
  "if" => [true, 1, 'a']
}

false_case = {
  "if" => [false, 1, 'a']
}


true_case_compiled = JSONLogic.compile(true_case)
false_case_compiled = JSONLogic.compile(false_case)

Benchmark.ips do |x|
  x.report("if_operator[true]") { true_case_compiled.evaluate(nil) }
  x.report("if_operator[false]") { false_case_compiled.evaluate(nil) }
end

Before PR

Warming up --------------------------------------
   if_operator[true]   120.624k i/100ms
  if_operator[false]   113.248k i/100ms
Calculating -------------------------------------
   if_operator[true]      1.183M (± 2.2%) i/s -      6.031M in   5.101916s
  if_operator[false]      1.159M (± 2.1%) i/s -      5.889M in   5.082047s

After PR

Warming up --------------------------------------
   if_operator[true]   164.110k i/100ms
  if_operator[false]   154.327k i/100ms
Calculating -------------------------------------
   if_operator[true]      1.642M (± 0.3%) i/s -      8.370M in   5.097412s
  if_operator[false]      1.533M (± 1.0%) i/s -      7.716M in   5.033156s

About 32% ~ 35% improvement

[fill32]

TIL: access an out-of-bound index will yield nil instead of an exception.

[fill32]

lg, very good on proactively working on these performance improvements.