Rewrite property based tests using `fast-check` instead of `jsverify`

👋 Hello,

This issue is mostly opened as a suggestion.

This project relies on `jsverify`, a library that is not maintained anymore. The suggestion is to migrate the tests written with `jsverify` to `fast-check`.

**Context**
jsverify's owner stopped the maintenance of the library more than a year ago. In addition, the last real commit to jsverify was on the 6th of September 2019.

**Benefits of `fast-check` over `jsverify`**
1. You don't need to define unmapping fuctions on your calls to `map` (`smap` in `jsverify`).
2. The arbitraries are able to find more bugs. _See attached PR_
3. There is a built-in way to handle commands.
4. Maintained.

I might have opened the PR a bit early but here is the PR: https://github.com/jlfwong/speedscope/pull/353

Review the proposed migration in pull request #353 and identify the property-based tests currently using jsverify. Compare their intended coverage with fast-check, then confirm that the tests run successfully after migration and that jsverify is no longer used for them.

Written by the indexing model from the issue text.