feat: sync back-references

[Sheraff]

DISCLAIMERS:

• this PR is a POC, code isn't very clean (the reference handling is done directly in the walkers, and not in its own neat plugin).
• this PR was just a toy idea initially, there is absolutely no issue with simply throwing the code away

---

Add support for back-references:

• support preserving identity of objects

  const a = {}
  const data = {
    foo: a,
    bar: a,
  }
  const res = tson.parse(tson.stringify(data))
  res.foo === res.bar // true

• support circular references

  const data = {}
  data.foo = data
  const res = tson.parse(tson.stringify(data))
  data === data.foo // true

This PR also includes

• changes in benchmark
  • use Intl.NumberFormat to format results
  • use process.memoryUsage to also log memory information (though I'm not sure how to interpret it, nor whether it's actually useful...)

This PR does not include

• changes to async methods (serialize / deserialize) to enable back-references in these cases too

[codecov]

Codecov Report

Attention: 20 lines in your changes are missing coverage. Please review.

Files	Coverage Δ
src/sync/serialize.ts	100.00% <100.00%> (ø)
src/sync/deserialize.ts	86.11% <78.26%> (-13.89%)	⬇️

... and 5 files with indirect coverage changes

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