Should be checked against official Rust API naming guidelines. LrukCache, not LRUKCache etc.

https://rust-lang.github.io/api-guidelines/naming.html#casin...

Would love to see benchmarks vs competition considering the high performance claim. Foyer is another rust hybrid cache, and quick-cache is the fastest in-memory impl I'm aware of.

Sane defaults and easy of setting a memory limit are two other things I look for in caches.

On your example, without reading into the implementation, I'm wondering if the comment is wrong, or if the comment is telling us about a hidden default, but then what does the 2 mean.

    // Create an LRU cache with a capacity of 100 entries
    let mut cache = LRUKCache::new(2);

Why 100? Why not 2?