iterators: 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/iterators/solution.md

@@ -3,3 +3,23 @@
 ```rust,editable
 {{#include exercise.rs:solution}}
 ```
+
+- **`cycle()`:** We create an iterator `b` that repeats the elements of `values`
+  infinitely. This handles the wraparound requirement elegantly without manual
+  index modulo arithmetic.
+- **`skip()`:** We advance the cycled iterator by `offset` positions.
+- **`zip()`:** We combine the original iterator `a` with the offset iterator `b`.
+  The `zip` function yields pairs of elements. Crucially, `zip` stops as soon as
+  either iterator is exhausted. Since `a` has the length of `values` and `b` is
+  infinite, the resulting zipped iterator has the same length as `values`.
+- **`map()` and `collect()`:** We calculate the difference for each pair and collect
+  the results into a new `Vec`.
+
+<details>
+
+- Mention that `values.iter()` creates an iterator that yields references (`&i32`).
+  In the `map` closure, we dereference them (`*b - *a`) to perform arithmetic.
+- This functional approach is often more concise and less error-prone (no off-by-one
+  index errors) than manual looping with indices.
+
+</details>