feat: added processAnchorRefund function

[Day-veed]

Description

Please include a summary of the change and which issue is fixed. Please also include relevant motivation and context. List any dependencies that are required for this change.

Fixes # (issue)
#88 Add processAnchorRefund function

Type of change

Closes #88 Add processAnchorRefund function

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

I added a Jest unit test suite in packages/anchor-service/src/index.spec.ts that covers all refund scenarios:

Test A: Full refund – Verifies a failed transaction is fully refunded and status updates to refunded
Test B: Partial refund – Verifies partial refund handling and status updates to partially_refunded
Test C: Skip when not failed – Verifies no refund is processed when transaction status isn’t failed
Test D: Refund executor failure – Verifies transaction status is set to refund_failed and error is rethrown
Test Configuration:

Framework: Jest with ts-jest
TypeScript: Strict mode enabled
Environment: Node
Dependencies: In-memory mocks for AnchorTransactionRepository and AnchorRefundExecutor
To run tests:
pnpm --filter @stellar-pay/anchor-service test

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

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[MissBlue00]

@Day-veed the ci/cd checks failed, please resolve