Add helper for deriving the storage key for a creator's holder balance

[Chucks1093]

Summary

The storage key for a creator's holder balance is constructed inline in multiple places across the contract. A shared helper should produce this key consistently so any future key format change only needs to be made in one place.

Scope

• Add holder_balance_key(creator_id: Address, holder: Address) -> Symbol helper
• Replace all inline holder balance key constructions with the helper
• Add unit tests confirming the helper produces the expected key format for two different creator/holder pairs

Acceptance Criteria

• Helper produces correct key format
• All inline constructions replaced
• Unit tests for two distinct creator/holder pairs
• Key format consistent with existing stored data (no migration needed)

ETA: 12 hours

---

Coordinate on Telegram

[Trusty08]

Hi maintainer, please i'll love to work on this issue please assign it to me. Thank you.

[emdevelopa]

@emdevelopa has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hii maintainer I will like to jump on this issue

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

[Johnsmichael150]

@Johnsmichael150 has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hey maintainer! I'd love to work on this issue, please assign it to me.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Johnsmichael150 to this issue.

[drips-wave]

Congratulations, @emdevelopa! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on July 30, 2026.

🧑‍💻 @emdevelopa: 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.

Warning

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.

🤠 Repo maintainers: Please keep an eye on the contributor's progress and review their work before the due date. You can manage this issue, including adjusting its complexity and points, here.

🌊 Happy Wave 🌊

[drips-wave]

This issue has been completed by @emdevelopa as part of the Stellar Wave Program's 7th Wave 🥳

😎 @emdevelopa: You earned 200 Points for completing this issue! After the current Wave ends, you'll be eligible for a percentage of the Wave's reward pool based on the percentage of total points you've earned. Learn more here. You can also Leave a review to share your experience working on this issue.

🧑‍💻 Repo maintainers: How'd the contributor do? Leave a review to share your experience working with them.