This PR introduces improvements to the Contrast class and its related tests:

Refactor:

• Simplified the Contrast::ratio method for better readability by extracting the luminance calculation into a dedicated Contrast::calculateLuminance method.
• Improved conditional checks for color conversion in the Contrast class to ensure cleaner and more concise code.

Added new tests to validate:

• Luminance calculations for edge cases (e.g., white and black colors).
• Adjusted existing test datasets for better precision and accuracy in contrast ratio calculations.

These changes improve the readability, maintainability, and accuracy of the contrast calculation logic.