Write Lending Pool Unit Tests

[sweetesty]

📌 Pull Request

🔗 Related Issue
Closes #25

📝 Description

• Adds comprehensive unit tests for the LendingPool smart contract
• Necessary to ensure contract correctness since bugs in smart contracts are immutable once deployed

🚀 Changes Made

• Testing:
  • Added unit tests for deposit functionality
  • Added unit tests for withdraw functionality covering both success and failure cases
  • Added unit tests for liquidity checks
  • All tests written using the Soroban test environment

🧪 Testing & Validation

• Tested locally
• No runtime errors
• All test cases passing
• Edge cases handled (insufficient liquidity, failed withdrawals, zero deposits)

⚠️ Breaking Changes

• No breaking changes

📋 Contributor Checklist (MANDATORY)

• I was assigned to this issue
• My code follows the project structure and conventions
• I have tested my changes thoroughly
• I did not introduce unnecessary dependencies
• I have linked the issue (Closes Write Lending Pool Unit Tests #25)
• This PR is ready for review

💡 Notes for Reviewer

• Key areas to review: deposit test cases, withdraw failure scenarios, liquidity check assertions
• Known limitations: None