feat: Implement blockchain indexer with deposit event processing

[testersweb0-bug]

Description

This PR implements a Soroban event indexer and deposit handler for the Nestera backend. It enables real-time tracking of blockchain activity by polling Soroban RPC events and processing deposit events into application state.

Closes #401
Closes #402

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Key Changes

1. Soroban Event Listener Daemon

• Implemented IndexerService with a @Cron(CronExpression.EVERY_5_SECONDS) job
• Polls Soroban RPC for new contract events
• Tracks lastProcessedLedger via IndexerState entity to ensure resumability after restarts
• Batched event requests across monitored contracts for improved efficiency

Stellar Service Enhancements

• Added retryable getEvents method
• Integrated RpcClientWrapper for failover across RPC endpoints

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2. Deposit Event Handler

• Implemented DepositHandler for "Deposit" events
• Decodes Soroban event payload to extract:
  • publicKey
  • amount
• Supports:
  • SHA256 topic matching
  • Direct symbol matching

Data Consistency

• Uses TypeORM transactions to ensure:
  • LedgerTransaction creation
  • UserSubscription balance updates
    are executed atomically

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3. Error Handling

• Introduced DeadLetterEvent queue
• Captures failed event processing for later inspection and recovery

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4. Test Coverage

• Added unit tests for:
  • IndexerService
  • DepositHandler
• Covered:
  • Event polling logic
  • Payload decoding
  • Failure scenarios

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Verification

npm test src/modules/blockchain/indexer.service.spec.ts
npm test src/modules/blockchain/event-handlers/deposit.handler.spec.ts

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Project	Deployment	Actions	Updated (UTC)
nestera	Ready	Preview, Comment	Mar 27, 2026 0:48am

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