fix: Circular dependencies

[micksatana]

Issue

pnpm helps in detecting circular dependencies. This is what it found.

node_modules/.pnpm/@fastify+fast-json-stringify-compiler@5.0.2/node_modules/@fastify/fast-json-stringify-compiler/index.js -> node_modules/.pnpm/@fastify+fast-json-stringify-compiler@5.0.2/node_modules/@fastify/fast-json-stringify-compiler/standalone.js -> node_modules/.pnpm/@fastify+fast-json-stringify-compiler@5.0.2/node_modules/@fastify/fast-json-stringify-compiler/index.js

Both files depending on each other; index.js requires standalone.js and vice versa. This can be fixed by moving the functions from the index.js to the standalone.js. Then require in one direction only.

Checklist

• run npm run test and npm run benchmark (no benchmark script in this project)
• tests and/or benchmarks are included (not changing functionality)
• documentation is changed or added (no change nor feature)
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

[micksatana]

Fixes #69