feat: unsafe string format

[nigrosimone]

This PR add the 'unsafe' string format. By default, fast-json-stringify escapes all strings. With the 'unsafe' format, the string isn't escaped. This has a potentially dangerous security issue. You can use it only if you are sure that your data doesn't need escaping. The advantage is a significant performance improvement.

Usage into the JSON schema

const stringify = fastJson({
  title: 'Example Schema',
  type: 'object',
  properties: {
    'code': {
      type: 'string',
      format 'unsafe'
    }
  }
})

benchmark (safe VS unsafe):

short string............................................. x 14,605,189 ops/sec ±3.85% (157 runs sampled)
unsafe short string...................................... x 693,266,405 ops/sec ±3.05% (187 runs sampled)

long string without double quotes........................ x 19,598 ops/sec ±3.48% (165 runs sampled)
unsafe long string without double quotes................. x 378,676,248 ops/sec ±2.95% (157 runs sampled)

long string.............................................. x 6,330 ops/sec ±5.32% (169 runs sampled)
unsafe long string....................................... x 555,420,885 ops/sec ±2.04% (167 runs sampled)

side note: this PR is the continuation of the #685 (cesco69 is my other account). #685 will be closed and I'll continue here

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

[gurgunday]

Did you know about #685

[nigrosimone]

@gurgunday

Did you know about #685

Yes. Read my PR side note:

side note: this PR is the continuation of the #685 (cesco69 is my other account). #685 will be closed and I'll continue here

[gurgunday]

Sorry saw on my phone, I see

[gurgunday]

lgtm

[ivan-tymoshenko]

lgtm. Nice job 👍

[ivan-tymoshenko]

Suggested change

	'code': {
	type: 'string',
	format 'unsafe'
	}
	'code': {
	type: 'string',
	format 'unsafe'
	}