Add Rust programming exercises to Code Playground

[niklasmarderx]

What

Add 10-15 Rust programming exercises to the Code Playground, similar to the existing Python/JavaScript/Java/TypeScript exercises.

Why

Rust is one of the fastest-growing languages and very popular among the target audience (programmers). The Code Playground already supports 4 languages — Rust would be a natural addition.

How

1. Look at src/data/programmingExercises.ts for the exercise format
2. Add a new RUST_EXERCISES array following the same pattern
3. Include exercises across difficulty levels:
   • Beginner: Hello World, variables, functions, basic types
   • Intermediate: ownership, borrowing, structs, enums, pattern matching
   • Advanced: traits, generics, error handling with Result
4. Each exercise needs: id, title, description, template, solution, difficulty
5. Register the new exercises in the exercise mode service

Note

The exercises are typing practice — users type the code, they don't run it. So focus on idiomatic Rust code that teaches good patterns.