[CONTRACT] Implement Asset "Description" Storage

[Sadeequ]

Goal: Provide more info for the UI (e.g., "Nigerian Naira").

Description: Store a short string description for each Symbol.

Task: Create a getter get_asset_description(asset: Symbol) -> String.

[MarcusDavidG]

@MarcusDavidG has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

I can handle this issue and will like to work on it please, kindly assign thank you.

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

[drips-wave]

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

🧑‍💻 @MarcusDavidG: 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 🌊