feat: improve contracts and expand test cases

[dinahmaccodes]

Description

The changes aim to improve test coverage, ensure correctness, and validate edge cases for the Ownable, Aggregator, Counter, and KillSwitch contracts. Below is a summary of the changes made:

1. test_ownable.cairo:

• Added tests to validate the Aggregator contract's functionality
• Added event emission tests to validate proper event handling

2. test_aggregator.cairo:

• Added tests to validate the Aggregator contract's functionality
• Added event emission tests to validate proper event handling
• Included negative test cases to handle invalid scenarios, such as unauthorized access and invalid inputs.

3. test_counter.cairo:

• Added tests to validate the Counter contract's functionality
• Added safe dispatcher tests to handle edge cases

4. test_killswitch.cairo:

• Added tests to validate the KillSwitch contract's functionality