Add Doxygen Documentation and Complete API/Test Comments

[enum-class]

Issue Description

1. Add Doxygen Documentation

I propose adding Doxygen documentation to enhance code readability and provide a comprehensive reference for the project. The documentation should cover the entire codebase, including:

• Adding Doxygen comments for all functions and methods
• Describing the purpose, parameters, return values, and usage examples
• Including Doxygen comments for classes, structures, and enums

2. Complete API Comments

Ensure that all API functions, classes, and structures have complete and informative comments. API comments should provide a clear understanding of the purpose, inputs, and outputs of each API element.

• Check and complete comments for all API functions
• Provide explanations for class members, structures, and enums
• Include any additional information relevant to API users

3. Complete Test Comments

Comments in test code are crucial for understanding the purpose of each test case, especially when troubleshooting or maintaining the test suite.

• Review and complete comments for all test cases
• Include explanations for test setups, assertions, and expected outcomes
• Ensure clarity and readability of the test comments