Fix: use Unsatisfiable for banned instances (unrestricted Monoid / Semigroup for linear containers)

[konn]

Currently, Prelude.Semigroup instance for (linear) HashMap / Set results in a runtime error.
This PR explicitly bans these instances by using Unsatisfiable type constraint family.

[treeowl]

You have multiple build failures. Unsatisfiable is only available with base-4.19.0.0. Before that, there are some other tricks you can play. Here's a nice version I wrote a while back.

[konn]

@treeowl Thank you for pointing it out! Then I will introduce compat module before/after GHC 9.8 and put your code (with naming tweaking) for older versions.

[konn]

Ah, indeed there is already one - `Prelude.Linear.Unsatisfiable. In this time, I just use them.

[aspiwack]

I'm not too sure about this. The message isn't suppose to ever reach the user, if the message surfaces it would be a bug in the library. Have you experienced this error message? (if so, please report a bug 🥺)

I don't actually remember why we have these instances to begin with. My best guess is that at some point, we'd decided that the Prelude's Semigroup class was a superclass to the linear Semigroup class. And so we'd absolutely needed a Prelude.Semigroup instance for Hashmaps if they were to have a linear Semigroup instance.

But maybe we don't need these instances. How about simply deleting them instead?

[treeowl]

An Unsatisfiable constraint on an instance serves two main purposes:

1. It documents (in the type error) that the instance is not unintentionally missing. This prevents, e.g., feature requests to have it added.
2. It ensures that no one wastes (further) time trying to write said instance. It can't be written and someone has checked carefully that that's the case.

[aspiwack]

Fair enough.

Are the messages I suggest clear enough? I haven't spend much time wordsmithing.

[konn]

@treeowl Thank you for clarifying the purpose of Unsatisfiable. Yes, that's exactly my intention to prevent illegal orphan instances.

@aspiwack Thanks! I think it looks good, and committed into the PR.