Issue #4631: Make Later covariant

[yanns]

Same as #937

fixes #4631

[satorg]

Thank you for the fix!
Note that Later is one of the Leaf descendants. The other two are Always and Now.
I wonder if it makes sense to make all the "leaves" covariant together rather than just one of them?
I feel it could be rather confusing to have one Leaf covariant and the other two invariant.

[yanns]

Thank you for the fix! Note that Later is one of the Leaf descendants. The other two are Always and Now. I wonder if it makes sense to make all the "leaves" covariant together rather than just one of them? I feel it could be rather confusing to have one Leaf covariant and the other two invariant.

I had the same thoughts when changing Later, but was not feeling confident enough to make more changes than the very strict necessary. Thanks for the quick feedback! I've now adapted all leafs of Eval.

[satorg]

@yanns , I lost tracking of your PR, sorry. Would you mind updating it to the most recent "main" such that we could re-run all the checks please? Thank you!

[yanns]

@satorg thanks for coming back! I've updated the branch. The tests on scala 2.12 with scala native are failing, without any good error message.

[yanns]

now all tests have passed

[satorg]

Thank you!

[yanns]

When does a PR get merged? I could find any process described in https://github.com/typelevel/cats/blob/main/CONTRIBUTING.md ?
Do you wait for 2 reviews?