Make it possible for elm-test to use core's Random

[mgold]

This adds Random.independentSeed, which allows the creation of random
seeds that are completely independent of each other. No amount of taking
random numbers from one seed will "wind" it to the same place as
another, such that they produce the same values.

This feature is essential to elm-test's ability to reproduce failures
because it allows each fuzz test to consume as many random values as it
needs without affecting tests that run after it. It means we can run
failing tests alone without disturbing the failure. It also makes it
possible to parallelize test runs.

If this PR is merged, elm-test will be able to use core's Random
implementation instead of my third party library. cc @rtfeldman

[process-bot]

Thanks for the pull request! Make sure it satisfies this checklist. My human colleagues will appreciate it!

Here is what to expect next, and if anyone wants to comment, keep these things in mind.

[process-bot]

Thanks for the pull request! Make sure it satisfies this checklist. My human colleagues will appreciate it!

Here is what to expect next, and if anyone wants to comment, keep these things in mind.

[basile-henry]

This looks pretty useful! 👍

[basile-henry]

unique

[mgold]

Force-pushed a commit that resolves both of @basile-henry's comments.

[mgold]

Force-pushed a commit that resolves both of @basile-henry's comments.

[evancz]

Is this on top of the increased randomness and addition of constant?

@mgold, can explain to me in Slack what needs to be done and why? I do not recall what this is all about.

[evancz]

Is this on top of the increased randomness and addition of constant?

@mgold, can explain to me in Slack what needs to be done and why? I do not recall what this is all about.

[evancz]

Ended up talking it through, and I understand the particular details and decisions now. Thank you @mgold! 😄

[evancz]

Ended up talking it through, and I understand the particular details and decisions now. Thank you @mgold! 😄