Use memcpy() to dump true/false/null (#736)
Use memcpy() to dump true/false/null (#736)

Maybe, the standard C library may use SIMD instructions,
so it is faster than our own code.

Similar:
- https://github.com/ohler55/oj/pull/734
- https://github.com/ohler55/oj/pull/674

−               | before | after  | result
--               | --     | --     | --
Oj.dump (macOS)  | 1.699M | 2.020M | 1.189x
Oj.dump (Linux)  | 1.849M | 2.260M | 1.222x

### Environment
- macOS
  - macOS 12.1
  - Apple M1 Max
  - Apple clang version 13.0.0 (clang-1300.0.29.30)
  - Ruby 3.1.0
- Linux
  - Zorin OS 16
  - AMD Ryzen 7 5700G
  - gcc version 11.1.0
  - Ruby 3.1.0

### macOS
#### Before
```
Warming up --------------------------------------
             Oj.dump   169.730k i/100ms
Calculating -------------------------------------
             Oj.dump      1.699M (± 0.7%) i/s -     25.629M in  15.089624s
```

#### After
```
Warming up --------------------------------------
             Oj.dump   201.206k i/100ms
Calculating -------------------------------------
             Oj.dump      2.020M (± 0.9%) i/s -     30.382M in  15.044372s
```

### Linux
#### Before
```
Warming up --------------------------------------
             Oj.dump   180.943k i/100ms
Calculating -------------------------------------
             Oj.dump      1.849M (± 1.1%) i/s -     27.865M in  15.072276s
```

#### After
```
Warming up --------------------------------------
             Oj.dump   224.695k i/100ms
Calculating -------------------------------------
             Oj.dump      2.260M (± 1.4%) i/s -     33.929M in  15.012352s
```

### Test code
```ruby
require 'benchmark/ips'
require 'oj'

data = {
  true: (0..10).map { true },
  false: (0..10).map { false },
  null: (0..10).map { nil },
}

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

  x.report('Oj.dump') { Oj.dump(data) }
end
```
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