Add examples of different styles of callbacks

Add an `## Examples` to each of the three callback articles with Rust + Deno TS examples of how the callbacks are used and utilised.

Find the three callback articles in the repository (likely under docs/ or a similar directory). Review existing Rust and Deno TypeScript examples in the project to understand the style. For each article, add an '## Examples' section with concise code snippets demonstrating callback usage. Ensure examples compile and follow the project's conventions.

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