[contract] Add 3 Tests to escrow_tests.rs (Part 2)

[Olowodarey]

📋 Overview

Expand test coverage for the escrow module by adding 3 new tests (Part 2 of 2).

✅ Tasks

• Add 3 new test functions to contract/tests/escrow_tests.rs
• Follow existing test patterns and helper functions
• Verify all tests pass

🧪 New Tests (3 total)

Test 1: Escrow Balance Tracking

#[test]
fn test_escrow_balance_tracking_accuracy() {
    // Lock multiple stakes
    // Release some payouts
    // Verify balance tracking is accurate throughout
}

Test 2: Escrow With Market Cancellation

#[test]
fn test_escrow_refund_on_market_cancellation() {
    // Lock stakes for market
    // Cancel market
    // Verify stakes are refunded
}

Test 3: Concurrent Escrow Operations

#[test]
fn test_concurrent_escrow_operations() {
    // Multiple users lock stakes simultaneously
    // Multiple users receive payouts simultaneously
    // Verify no race conditions or balance issues
}

🔍 Verification

• All 3 tests written
• All tests pass
• Tests follow existing patterns
• No clippy warnings

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