Refactor question utils for enhanced performance and readability

[djeada]

• Renamed p to README_PATH for clarity.
• Introduced EXERCISES_PATH for the exercises directory.
• Precompiled regex patterns for efficiency.
• Changed get_file_list to get_file_content and made it return a string directly.
• Used UTF-8 encoding when opening files.
• Simplified get_question_list and get_answered_questions by using list comprehensions and conditional checks.
• Updated type hints for better clarity.
• Removed unused variables and optimized function logic.
• Ensured all functions read the file content once when needed.
• Enhanced the docstring example for accuracy.
• Maintained all original functionalities and interfaces for backward compatibility.