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/02-generic-structs/README.md

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+# Generic Message Queue
+
+Build a message queue system that can handle different types of messages. You'll create generic structs and enums that can queue up emails, notifications, tasks, or any other message type without code duplication.
+
+## What you'll practice
+
+- Defining generic structs that hold collections of any type
+- Creating generic enums for different message states
+- Writing implementation blocks with generic type parameters
+- Using associated functions vs instance methods with generics
+
+## Further information
+
+- [Generic Data Types](https://doc.rust-lang.org/book/ch10-01-syntax.html)
+- [Method Definitions](https://doc.rust-lang.org/book/ch05-03-method-syntax.html)