[9.x] Makes ModelNotFoundException generic

[nunomaduro]

The contributor of this pull request is @spawnia, I've just made a few tweaks.

This pull request makes the ModelNotFoundException generic. So, in theory, once Eloquent is generic too, we will be able to do stuff like this:

try {
    User::findOrFail(1);
} catch (ModelNotFound $e) {
    $e->getModel()::myUserMethod(); // --> autocompletion, and static analysis support here.
}

[spawnia]

I would have preferred array<int>|array<string> for two reasons.

1. The type of a model ID should be monomorpic.
2. The key of this array does not matter here, an associative array works just as well.

[spawnia]

Constructing this class generically is always going to be awkward, since the generic type can not be derived from the constructor arguments. Perhaps it can be considered to move the arguments that are currently passed to setModel() into the constructor for the next major version of Laravel?

[spawnia]

The ID type could be made generic too.

[spawnia]

Thanks @nunomaduro for getting this merged. Perhaps we can iterate on it some more, although the biggest possible improvement to this would allowing inference of the generics through constructor arguments - this would require breaking changes.