[DOCS] Docs: Add Inline Rustdoc Comments for Invoice Token Storage Structures

[chizzy192]

[DOCS] Issue

Metadata

Field	Value
Domain	Docs
Difficulty	Easy (2 Days)
Effort Estimate	effort: 2h
Priority	P3-Low
Labels	good first issue, documentation
Target Branch	dev
Depends On	None

🎯 Context & Goal

Clear developer documentation accelerates open-source contribution and SDK integration.

This issue enhances documentation for contracts/invoice-token in storage.rs.

Accurate documentation ensures developers can seamlessly build on top of StellarSettle contracts.

📂 Target Files

• contracts/invoice-token/storage.rs → docs

📋 Implementation Tasks

• Task 1: Write/update documentation in contracts/invoice-token/storage.rs.
• Task 2: Ensure markdown formatting adherence.
• Task 3: Link to relevant source files and functions.

🛠️ Technical Guidance

('<!-- Documentation Snippet -->\n## API Reference\nDescribes public contract entrypoints.',)

🔗 References & Related

• Target doc: contracts/invoice-token/storage.rs

⏳ Delivery Window

This issue should be completed within 2 day(s) of assignment.

Contribution Workflow

1. Branch off dev: git checkout -b feature/issue-implementation dev
2. Implement all tasks in the checklist above.
3. Run all CI checks locally (see DEVELOPMENT.md).
4. Open a Pull Request targeting dev.
5. Link this issue in your PR description.

✅ Acceptance Criteria

• All implementation tasks above are completed cleanly.
• Code compiles without warnings or errors.
• All existing tests continue to pass.
• New unit tests cover all modified code paths.
• PR strictly targets the dev branch.
• Code follows project style guidelines (cargo fmt and cargo clippy).