[FEATURE] Add contract unit test suite: no tests exist for any contract

[derbydaniels9-cpu]

Summary

There are no contract unit tests. Without a test suite, there is no way to verify that the savings lock contract correctly enforces maturity dates, penalty calculations, or target amount conditions before deployment to mainnet.

Impact

A bug in the withdrawal logic (e.g. penalty not applied on early exit, or lock not enforced) directly causes financial loss — either to users or to the protocol.

Proposed test setup using the Soroban test framework

// tests/savings_lock_test.rs
#[cfg(test)]
mod tests {
    use soroban_sdk::{testutils::Address as _, Env, Address};
    use crate::SavingsLockContract;

    #[test]
    fn test_early_withdrawal_applies_penalty() {
        let env = Env::default();
        let contract_id = env.register_contract(None, SavingsLockContract);
        let user = Address::generate(&env);
        // deposit with 30-day lock
        // attempt withdrawal on day 5
        // assert penalty of 10% was applied
        // assert net payout = amount * 0.9
    }

    #[test]
    fn test_withdrawal_blocked_before_maturity() { ... }

    #[test]
    fn test_full_withdrawal_after_maturity_no_penalty() { ... }

    #[test]
    fn test_target_lock_blocked_before_target_reached() { ... }
}

Coverage targets

• All lock types: FLEXIBLE, FIXED, TARGET
• Early withdrawal penalty
• Maturity date enforcement
• Interest accrual accuracy
• Edge case: deposit of 0 should be rejected

Files affected:

• New: tests/savings_lock_test.rs