five terrible horseman of making unsafe Rust collections

• 0013.1 Scrapped 🦀
• https://rust-unofficial.github.io/too-many-lists/sixth-variance.html

• There are five terrible horsemen of making unsafe Rust collections:

• Variance

• Drop Check
• NonNull Optimizations
• The isize::MAX Allocation Rule
• Zero-Sized Types

Mercifully, the last 2 aren't going to be a problem for us.