[CONTRACTS] Add helper for fetching current Stellar ledger timestamp from Horizon RPC

[chizzy192]

Metadata

Field	Value
Domain	Contracts
Difficulty	Easy (1–2 Days)
Effort Estimate	effort: 3h
Priority	P2-Medium
Labels	good first issue, easy, Stellar Wave
Target Branch	dev
Depends On	#131

🎯 Context & Goal

To compare invoice due dates against on-chain Stellar time, backend services need to fetch the latest closed ledger timestamp from Horizon / Soroban RPC rather than relying on local server system time.

This issue adds fetchLatestLedgerTimestamp(): Promise to src/services/stellar/horizon-client.service.ts.

📂 Target Files

• src/services/stellar/horizon-client.service.ts -> Fetch ledger timestamp helper

📋 Implementation Tasks

• Implement fetchLatestLedgerTimestamp() using Horizon Server.ledgers().order("desc").limit(1).call()
• Extract closed_at ISO timestamp string and convert to Unix epoch seconds
• Add unit tests mocking Horizon ledgers response

🛠️ Technical Guidance

const ledgers = await server.ledgers().order('desc').limit(1).call();
return Math.floor(new Date(ledgers.records[0].closed_at).getTime() / 1000);

🔗 References & Related

• Stellar Horizon API Ledgers Endpoint

⏳ Delivery Window

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

Contribution Workflow

1. Branch off dev: git checkout -b feature/descriptive-name 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: Closes #XX.

✅ Acceptance Criteria

• All implementation tasks above are completed.
• Code compiles/builds without errors.
• All existing tests continue to pass.
• New tests are added with >80% coverage of new code.
• Code follows project style guidelines (formatting, linting).
• PR targets dev branch (NOT main).
• PR description references this issue.
• Documentation is updated if public API changed.

[Peaostrel]

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

i can handle this quickly

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