Rust 1.100.0 stabilizes custom allocators and the never type

Rust 1.100.0 lands with stabilized custom allocators, the never type, and extern "custom". Cargo gains its own linting system with an unused-dependency check and minimum publish age (dependency cooldowns). Platform support expands: wasm32-wasip3 reaches Tier 2, and a new Tier 3 target for the PS3 appears. Compatibility notes flag changed closure captures in if let, Infallible becoming an alias for !, and a new build artifact directory layout.