methods-and-traits: add explanatory commentary to solution

This commentary, written by Gemini, focuses on aspects of the solution that differ from the baseline languages (C/Java/Python), highlighting Rust-specific idioms and concepts.

Author: mgeisler

src/methods-and-traits/solution.md

@@ -3,3 +3,23 @@
 ```rust,editable
 {{#include exercise.rs:solution}}
 ```
+
+- **Trait Implementation:** We implement the `Logger` trait for `VerbosityFilter`,
+  matching the signature defined in the trait.
+- **Composition and Delegation:** The `VerbosityFilter` struct wraps another
+  logger (the `inner` field). In its implementation of `log`, it adds logic
+  (the verbosity check) and then delegates the actual logging to the inner logger
+  if appropriate.
+- **Wrapper Pattern:** This demonstrates how to extend behavior by wrapping a
+  type. In this specific case, `VerbosityFilter` is hardcoded to wrap
+  `StderrLogger`, but in real-world Rust code, `inner` would typically be generic
+  over any type that implements `Logger`.
+
+<details>
+
+- Note that `self.inner.log(...)` works because `StderrLogger` also implements
+  `Logger`.
+- Point out that this wrapper adds functionality (filtering) without modifying
+  the inner logger's code. This is a key benefit of using traits and composition.
+
+</details>