[CONTRACTS] Add structured log for Soroban contract event ingestion with ledger number and topic

[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	#135

🎯 Context & Goal

When the event indexer worker ingests on-chain contract events from Soroban RPC getEvents, structured logs must be emitted via Winston logger to facilitate operational monitoring in Datadog or CloudWatch.

This issue adds structured logging in src/services/stellar/event-indexer.service.ts recording ledgerSequence, contractId, topicSymbol, and eventPayload.

📂 Target Files

• src/services/stellar/event-indexer.service.ts -> Log event ingestion

📋 Implementation Tasks

• Add logger.info() call upon receiving each valid contract event
• Include metadata fields: ledgerSequence, contractId, topic, txHash
• Add unit tests verifying logger output format

🛠️ Technical Guidance

logger.info('Soroban event ingested', { ledgerSequence, contractId, topic, txHash });

🔗 References & Related

• Winston Structured Logging

⏳ 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.

[vstudio79]

@vstudio79 has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hi maintainer, can I take on the task of handling this?

ℹ️ Repo Maintainers: To accept this application, review their application or assign @vstudio79 to this issue.