generic types, traits and lifetimes

- get claude to create rustlings style exercises based on chapter 10 of the book
- update CLAUDE.md to prevent it from producing incorrect exercises
- complete exercises/01-generic-cache-system

exercises/04-generic-methods/README.md

@@ -0,0 +1,15 @@
+# Generic Methods & Implementations
+
+Build a generic data transformer that can convert, filter, and manipulate collections of any type. You'll practice writing methods on generic structs and using multiple type parameters in implementation blocks.
+
+## What you'll practice
+
+- Writing methods for generic structs with `impl<T>` blocks
+- Using multiple type parameters in methods like `<T, U>`
+- Associated functions vs instance methods on generic types
+- Method chaining with generic return types
+
+## Further information
+
+- [Method Syntax](https://doc.rust-lang.org/book/ch05-03-method-syntax.html)
+- [Generic Data Types](https://doc.rust-lang.org/book/ch10-01-syntax.html)