feat: Add contract upgrade proxy pattern

[cypriannwokolo2-creator]

Description

Contracts deploy once and are immutable. We need a proxy pattern for upgradability while preserving state.

Requirements

• Implement upgrade proxy in common/src/upgrade.rs
• Add set_implementation admin function
• Ensure state is stored in proxy, not implementation
• Add tests for upgrade lifecycle

Acceptance Criteria

• Proxy contract delegates to implementation
• Admin can upgrade implementation address
• State preserved across upgrades
• Tests verify upgrade behavior

Priority

Medium

[Fading-Dev]

@Fading-Dev has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hello maintainer I would like to work on this

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

[Femaleotaku]

@Femaleotaku has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi, I'd like to take this on.

I'll implement this following the existing conventions in the codebase, keeping the change focused and well-tested.

Planned approach, based on the acceptance criteria:

• Proxy contract delegates to implementation
• Admin can upgrade implementation address
• State preserved across upgrades
• Tests verify upgrade behavior

Happy to get started right away if assigned — looking forward to contributing.

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

[webdevayo]

@webdevayo has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi maintainer I have thoroughly read the description to this issue and I can resolve this according to the description required ensuring it meet all the acceptance criteria kindly assign..

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

[dimin4241-svg]

@dimin4241-svg has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

I have experience with Soroban upgrade and proxy patterns, including admin authorization and state-preserving migrations. I reviewed this issue and can keep the implementation narrow, document the upgrade boundary, and verify that existing storage survives an upgrade. I can deliver a focused change within 2–3 days of assignment. Please assign it to me.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @dimin4241-svg to this issue.

[drips-wave]

Congratulations, @Femaleotaku! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on August 31, 2026.

🧑‍💻 @Femaleotaku: 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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