[Accepted] SE-0374: Add `sleep(for:)` to Clock

Hi all,

The twice-extended review for SE-0374: Add sleep(for:) to Clock ran from October 11 to November 22. The language workgroup has decided to accept the proposal.

Feedback was light but entirely positive for the feature; the repeated extensions were to further build out the API surface for orthogonality purposes.

Thank you to all who participated in the review, and to the authors for sticking through a protracted review!