improve performance of safeParse

[Uzlopak]

before:
JSON.parse x 1,711,391 ops/sec ±0.86% (87 runs sampled)
JSON.parse proto x 1,077,100 ops/sec ±1.18% (90 runs sampled)
secure-json-parse parse x 1,430,832 ops/sec ±1.00% (91 runs sampled)
secure-json-parse parse proto x 1,576,912 ops/sec ±1.14% (84 runs sampled)
secure-json-parse safeParse x 1,420,410 ops/sec ±1.06% (87 runs sampled)
secure-json-parse safeParse proto x 139,151 ops/sec ±0.97% (90 runs sampled)
JSON.parse reviver x 497,298 ops/sec ±0.83% (90 runs sampled)

after:
JSON.parse x 1,738,271 ops/sec ±0.84% (88 runs sampled)
JSON.parse proto x 1,100,147 ops/sec ±1.23% (89 runs sampled)
secure-json-parse parse x 1,441,809 ops/sec ±0.79% (91 runs sampled)
secure-json-parse parse proto x 1,592,567 ops/sec ±0.82% (82 runs sampled)
secure-json-parse safeParse x 1,405,980 ops/sec ±1.30% (90 runs sampled)
secure-json-parse safeParse proto x 917,157 ops/sec ±0.81% (92 runs sampled)
JSON.parse reviver x 501,752 ops/sec ±0.78% (88 runs sampled)

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

[mcollina]

linting is failing

[mcollina]

Is this a semver-major change?

[Uzlopak]

@mcollina

Should not be backwards breaking. I just corrected the typings of scan.

[mcollina]

lgtm

[mcollina]

Can you send a PR to fastify to use this instead? It should improve things in case of a failure.