soroban-contracts: Build storage migration utilities for versioned models

[manoahLinks]

Create migration helpers for safe state upgrades between schema versions.

[jaynomyaro]

@jaynomyaro has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

Hi! I’m a full-stack developer with a strong blockchain background. I’d love to handle this issue and can deliver a clean, reliable solution. Kindly assign it to me.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @jaynomyaro to this issue.

[drips-wave]

Congratulations, @jaynomyaro! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on April 29, 2026.

🧑‍💻 @jaynomyaro: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

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When opening a PR, please link it to this issue to ensure it gets tracked accurately. Points are awarded when this issue is marked as completed by the maintainer.

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