[contract] Add 3 Tests to market_tests.rs (Part 1)

[Olowodarey]

📋 Overview

Expand test coverage for the market module by adding 3 new tests (Part 1 of 2).

✅ Tasks

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

🧪 New Tests (3 total)

Test 1: Create Market With Multiple Outcomes

#[test]
fn test_create_market_multiple_outcomes() {
    // Create market with 3+ outcomes
    // Verify all outcomes are stored
    // Verify predictions can be made on any outcome
}

Test 2: Market Expiration

#[test]
fn test_market_expiration() {
    // Create market with end_time
    // Advance time past end_time
    // Try to make prediction
    // Should fail with market expired error
}

Test 3: Cancel Market

#[test]
fn test_cancel_market() {
    // Create market with predictions
    // Cancel market
    // Verify market is marked cancelled
    // Verify refunds are processed
}

🔍 Verification

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

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