test: Add property-based tests

[dubzzz]

Following the discussion started on #79. I'm opening this PR as an opened question and suggestion to better cover the library and its edge-cases.

Feel free to close it 👍

---

First, what is property-based testing? It's a technic coming from functional world and aiming to help devs into detecting edge cases without having them to think of them too much.

Why, property-based testing? Well, in order to reduce the risks of bugs and potentially regressions on key libraries.

Could it found problems? Well, probably. I tried another property but I'm not sure whether or not the failure is considered as ok or not. As such I'm not sure of what to expect from truncate so I was not able to make a decision.

it('produces strings with at most <truncate> characters', () => {
  fc.assert(
    fc.property(
      fc.anything({
        withBigInt: true,
        withBoxedValues: true,
        withDate: true,
        withMap: true,
        withNullPrototype: true,
        withObjectString: true,
        withSet: true,
        withSparseArray: true,
        withTypedArray: true,
        withUnicodeString: true,
      }),
      fc.nat(),
      (source, truncate) => {
        const output = inspect(source, { truncate })
        expect(output).to.have.lengthOf.at.most(truncate)
      }
    )
  )
})

Who am I? I'm the author of fast-check, the library added by this PR. It's the leading property-based testing library today.