[contract] Add 3 Tests to config_tests.rs

[Olowodarey]

📋 Overview

Expand test coverage for the config module by adding 3 new tests.

✅ Tasks

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

🧪 New Tests (3 total)

Test 1: Pause and Unpause Contract

#[test]
fn test_pause_and_unpause_contract() {
    // Initialize contract
    // Pause contract
    // Verify operations fail
    // Unpause contract
    // Verify operations succeed
}

Test 2: Update Platform Fee

#[test]
fn test_update_platform_fee() {
    // Initialize contract with fee
    // Update platform fee
    // Verify new fee is applied
}

Test 3: Config Access Control

#[test]
fn test_config_update_unauthorized() {
    // Try to update config as non-admin
    // Should fail with authorization error
}

🔍 Verification

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

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