docs(invoice-token): add inline rustdoc documentation for storage keys, structures, and TTL policies in storage.rs

[chizzy192]

Context & Problem Statement

The storage management layer in contracts/invoice-token/src/storage.rs defines core ledger keys for balances, allowances, nonces, admin roles, and transfer locks. Currently, the module lacks comprehensive module-level documentation and inline /// rustdoc comments explaining key data shapes, lifecycle conventions, and Soroban storage TTL bump policies.

This issue adds exhaustive documentation across the entire storage module.

Architectural Motivation & Technical Requirements

• In contracts/invoice-token/src/storage.rs:
  • Add //! module-level documentation explaining the storage architecture.
  • Add /// documentation to every StorageKey variant detailing:
    • Purpose of the key.
    • Data type stored in persistent vs instance storage.
    • Read/write access patterns and TTL bump requirements.
  • Add /// documentation to all public helper functions explaining parameters, return values, and failure modes.

Acceptance Criteria

• Every StorageKey variant documented with rustdoc comments.
• All public functions in storage.rs have doc comments.
• cargo doc --no-deps -p invoice-token compiles without warnings.

Target Branch: dev
Estimated Effort: 1–4 hours | Delivery: 1–2 days
Difficulty: Easy

[npmInstallRegret]

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

hi, i would like to work on this.

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

[Danitello123]

@Danitello123 has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Please kindly assign me this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Danitello123 to this issue.

[frank0277]

@frank0277 has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi maintainer please i would like to work on this

ℹ️ Repo Maintainers: To accept this application, review their application or assign @frank0277 to this issue.

[uche102]

@uche102 has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi maintainer please i would like to work on this

ℹ️ Repo Maintainers: To accept this application, review their application or assign @uche102 to this issue.

[drips-wave]

Congratulations, @Danitello123! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on August 31, 2026.

🧑‍💻 @Danitello123: 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 🌊