This commit refactors the initial implementation to fit into std and
makes some other changes:
- use MaybeUninit internally in SyncOnceCell
- correctly impl Drop for lazy::Once
- port Lazy::take from once_cell from: https://github.com/matklad/once_cell/pull/100
Co-Authored-By: Paul Dicker <pitdicker@users.noreply.github.com>