[10.x] Add Conditionable trait to Sleep class

[bradietilley]

From #47092

This PR adds the Conditionable trait to the Sleep class. Example:

Sleep::for(1)->second()
    ->unless(
        $some->status === SomeStatus::PENDING,
        fn (Sleep $sleep) => $sleep->and(500)->milliseconds()
    );

[nunomaduro]

Personally feel that it's very unlikely that people would want todo something like this. However, on the other hand, it would be cool "cancel" the pause doing something like:

Sleep::for(1)->second()->unless($task->completed());

As usual, let's wait to see what Taylor thinks.

[bradietilley]

I like that syntax.

Sleep::for(1)->second()->unless($task->completed());
// or
Sleep::for(1)->second()->when($task->pending());

I can move https://github.com/bradietilley/framework/pull/1/files into this PR if the above syntax is preferred.

[taylorotwell]

Yeah personally like the syntax suggested by Nuno a bit better.