Refactor in where obtain hash keys by using common function

[Watson1978]

Refactor in where obtain hash keys by using common function. However, it might have the margin of error for the overhead of calling oj_calc_hash_key().

−	before	after	result
Oj.dump	449.521k	447.738k	0.996x

Environment

• Linux
  • Manjaro Linux x86_64
  • Kernel: 6.3.5-2-MANJARO
  • AMD Ryzen 7 5800H
  • gcc version 13.1.1
  • Ruby 3.2.2

Before

Warming up --------------------------------------
             Oj.load    44.738k i/100ms
Calculating -------------------------------------
             Oj.load    449.521k (± 0.9%) i/s -      6.755M in  15.029388s

After

Warming up --------------------------------------
             Oj.load    44.117k i/100ms
Calculating -------------------------------------
             Oj.load    447.738k (± 0.3%) i/s -      6.750M in  15.075672s

Test code

require 'bundler/inline'
gemfile do
  source 'https://rubygems.org'
  gem 'benchmark-ips'
  gem 'oj'
end

json =<<-EOF
{
  "$id": "https://example.com/person.schema.json",
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "title": "Person",
  "type": "object",
  "properties": {
    "firstName": {
      "type": "string",
      "description": "The person's first name."
    },
    "lastName": {
      "type": "string",
      "description": "The person's last name."
    },
    "age": {
      "description": "Age in years which must be equal to or greater than zero.",
      "type": "integer",
      "minimum": 0
    }
  }
}
EOF

Benchmark.ips do |x|
  x.warmup = 5
  x.time = 15

  x.report('Oj.load') { Oj.load(json, mode: :compat) }
end

[ohler55]

A further optimization would be to remove line 19 then line 21 becomes:
if (Qundef == val->key_val && Yes == pi->options.create_ok && NULL != pi->options.create_id &&
and the new line 28 becomes volatile VALUE rkey = oj_calc_hash_key(pi, kval);.

Since oj_calc_hash_key already gets rkey from the parent the suggested change avoids the assignment and stack variable us in the first block.

[Watson1978]

Thanks for your review. I have fixed the codes to follow the suggestion.