Add RB_UNLIKELY hint for tracing log

[Watson1978]

I think that Yes == pi->options.trace will be false in most cases.
If the compiler supports it, the UNLIKELY hint might speed up the conditional branching slightly.

−	before	after	result
Oj.load	374.821k	383.001k	1.022x

Environment

• Linux
  • Manjaro Linux x86_64
  • Kernel: 5.18.0-1-rt11-MANJARO
  • AMD Ryzen 7 5700G
  • gcc version 12.1.0
  • Ruby 3.1.2

Before

Warming up --------------------------------------
             Oj.load    37.784k i/100ms
Calculating -------------------------------------
             Oj.load    374.821k (± 0.5%) i/s -      7.519M in  20.060807s

After

Warming up --------------------------------------
             Oj.load    38.599k i/100ms
Calculating -------------------------------------
             Oj.load    383.001k (± 0.5%) i/s -      7.681M in  20.055707s

Test code

require 'benchmark/ips'
require 'oj'

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 = 10
  x.time = 20

  x.report('Oj.load') { Oj.load(json) }
end