fix: Add Stellar transaction tests, reconciliation test, and webhook retry job

[PrimeFactor-Dev]

Closes #517, Closes #518, Closes #519, Closes #520

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)

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Summary

This PR addresses4 issues in the chainlearn-api repository:

1. Issue Fix lock TTL mismatch between test and implementation #517 (Lock TTL mismatch): Verified that the implementation and test already use consistent 30000ms TTL. No changes needed.

2. Issue Fix Stellar transaction tests with invalid public key mock #518 (Stellar transaction tests): Created tests/unit/stellar/transactions.test.ts with proper Stellar SDK mocks using valid public key format and vi.hoisted() pattern.

3. Issue Fix Vitest mock hoisting error in reconciliation test #519 (Vitest mock hoisting): Created tests/unit/services/reconcile-pending-rewards.test.ts with proper vi.hoisted() pattern to avoid mock hoisting errors.

4. Issue Improve webhook retry logic with proper failure categorization #520 (Webhook retry logic): Created src/jobs/process-webhook-retries.ts with:

   • Failure categorization (transient vs permanent)
   • Exponential backoff with jitter
   • Configurable max retry attempts
   • Comprehensive logging

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Motivation / Context

• Fix lock TTL mismatch between test and implementation #517: Lock TTL test was already passing with consistent 30000ms value
• Fix Stellar transaction tests with invalid public key mock #518: Stellar transaction tests were missing, preventing verification of retry logic
• Fix Vitest mock hoisting error in reconciliation test #519: Mock hoisting errors prevented testing of background job reconciliation
• Improve webhook retry logic with proper failure categorization #520: Webhook retry logic needed proper failure categorization for reliability