[Lambda] Rust SDK for Durable Functions

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**Tell us about your request**

Rust SDK support for [Durable Functions](https://aws.amazon.com/about-aws/whats-new/2025/12/lambda-durable-multi-step-applications-ai-workflows/) - even basic support for just `step` and `wait` would be great, and `waitForCallback` would be a stretch goal!

**Which service(s) is this request for?**

Lambda Durable Functions

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**

We use Rust exclusively in our Lambda runtimes, and would like to take advantage of Durable Functions soon.

**Are you currently working around this issue?**

We're not, we're currently blocked from adopting Durable Functions in our Rust codebases.

Commencez par le lien vers Durable Functions dans l’issue et définissez les points d’entrée du Rust SDK nécessaires pour step et wait ; considérez waitForCallback comme un objectif complémentaire. La tâche serait considérée comme terminée si la prise en charge du périmètre convenu fonctionne, mais cette issue de roadmap ne nomme aucun fichier, test ou point d’entrée d’implémentation.

Rédigé par le modèle d'indexation à partir du texte de l'issue.