Don't stop early: Case-folding source code at memory speed

This post details significant performance optimizations for case folding, particularly for ASCII characters, by removing early exits and optimizing for vectorization. It introduces a branchless ASCII folding implementation that achieves memory bandwidth speeds (>45 GiB/s) by eliminating branches and leveraging vectorization. The post also covers efficient handling of Unicode case folding and memory management to avoid unnecessary allocations, including a strategy for allocating a worst-case buffer once for Unicode folds that might increase string length. The open-sourced Rust crate `casefold` implements these optimizations.