fast solutions to all Codewars katas written in Rust

it's not enough to solve a problem, it needs to be solved well

• nontrivial katas have benchmarks to easily compare solutions

• usage of third-party libraries is allowed even if not accepted by Codewars

• solutions are safe, meaning that they will panic or return nonsense on nonsense input rather than causing undefined behavior; nevertheless, there are 102 unsafe blocks

• even though most tests on Codewars contain only ASCII input, they use Rust's standard UTF-8–encoded strings, so solutions for string katas are made for Unicode input; nevertheless, .bytes()|.as_bytes()|.as_mut_vec() are used 77 times

• proposed function signatures and names are preserved; but are clippy-adjusted

• (large) lookup tables aren't generally allowed

• 8 kyu
• 7 kyu

• 6 kyu
• 5 kyu
• 4 kyu
• 3 kyu
• 2 kyu
• 1 kyu