yesdisown/numx ? reverse-engineered prompt

Build me a simple Rust command line app for practicing quick and accurate math.

I want it to quiz me with random arithmetic problems, let me answer in the terminal, and then tell me right away if I was correct. It should keep score, track how fast I answer, and help me improve over time by showing basic stats at the end of a round. Make it feel snappy and easy to use, with clear prompts and simple commands to start a practice session.

If it makes sense, add a few difficulty levels so I can choose easier or harder questions, and let me practice different kinds of math like addition, subtraction, multiplication, and maybe mixed mode. Keep it focused on the CLI experience, no fancy UI needed. If you need to look up current Rust docs or best practices, go ahead.