test: register and wire reentrancy fault-injection tests

[senmalong]

Pull Request Template

📝 Description

This PR registers and enables the hostile token reentrancy fault-injection test suite in quicklendx-contracts/src/lib.rs.

🎯 Type of Change

• Security enhancement
• Documentation update

🔧 Changes Made

Files Modified

• quicklendx-contracts/src/lib.rs
• TODO.md

Key Changes

• Registered test_reentrancy and test_reentrancy_fault_injection modules under #[cfg(all(test, feature = "legacy-tests"))].
• Updated TODO.md to reflect the completed tasks.

🧪 Testing

• Unit tests pass (the new tests have been wired and verified locally, though note other unrelated failures on main remain)
• Edge cases tested

📋 Contract-Specific Checks

• Soroban contract builds successfully
• Security considerations reviewed
• Contract functions tested

🔗 Related Issues

None (Issues are disabled in the repository)

🧪 How to Test

Execute tests with the legacy features enabled:

cargo test --features legacy-tests test_reentrancy_fault_injection