Implement E2E Integration Tests with Local Soroban Network

[RuthChisom]

Summary

Introduces a full end-to-end (E2E) test suite for the Soroban-based system, enabling real-world validation of contract behavior using a local network.

Changes

• Added script to spin up a local Soroban network using Docker

• Implemented E2E test covering:

  • Task registration
  • Keeper polling simulation
  • Execution verification

• Added retry mechanism to ensure reliable test execution

• Integrated E2E tests into GitHub Actions workflow

How to Test

Locally:

1. Run:
   bash scripts/start-soroban.sh
2. Execute:
   npm test

CI:

• Automatically runs on push and pull requests

Notes

• Tests are fully isolated and do not modify contract logic
• Designed to be deterministic and avoid flaky timing issues
• Improves confidence in real-world contract behavior

Related Issue

Closes #100

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