Feat/security upgrade tests

[Greymantron]

Closes #275, Closes #276, Closes #277, Closes #278

Summary of Changes

• Unauthorized Access Tests (. Add security test for unauthorized access #275): Added security tests in tests/integration/security_auth_tests.rs to verify that admin functions (mint, grant_role, pause) revert when called without the correct authorization.
• Overflow/Underflow Tests (. Add security test for overflow/underflow #276): Added security tests in tests/unit/security_arithmetic_tests.rs to ensure that balance subtractions and maximum supply checks revert appropriately, preventing underflow and overflow vulnerabilities.
• Reentrancy Protection Tests (. Add security test for reentrancy #277): Added tests in tests/integration/security_reentrancy_tests.rs utilizing a mock malicious contract to verify that the environment successfully protects against reentrant calls during state changes.
• Contract Upgrade Tests (. Add test for contract upgrade mechanism #278): Added integration tests in tests/integration/upgrade_tests.rs to verify that the contract upgrade mechanism executes correctly and preserves state variables like user balances across upgrades.

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