ISSUE#39 :Add negative scoring to score calculation

[23f3001526]

📌 What does this PR do?

Implements negative marking in the quiz score calculation.
Users are now awarded:

• +1 for each correct answer
• -0.25 for each incorrect answer
• 0 for unanswered questions

🔗 Related Issue

Fixes #39 : Allow negative marking for wrong answers

🔧 Type of Change

• Bug fix (non-breaking change)
• New feature
• Breaking change
• Documentation update

✅ How Has This Been Tested?

• Tested locally by running the HTML file using Live Server in VSCode
• Selected combinations of correct, incorrect, and unanswered questions to verify logic
• Example test: 2 correct, 1 wrong, 7 unanswered = Total score: 1.75 (working as expected)

Environment:

• OS: Windows 10
• Browser: Chrome 116
• Node: Not applicable (pure frontend change)

📸 Screenshots (if UI changed): showing a score of 1.75/10 for two correct answers and one wrong answer and rest unanswered out of 10 questions

📊 Impact / Performance

• No new dependencies introduced
• Minimal impact, as logic change is confined to a single JavaScript function (script.js)

✅ Checklist

• I have followed the code style guidelines.
• I have self-reviewed my code.
• I have commented on complex parts of the code.
• I have updated or added documentation where necessary.
• All tests pass locally.
• No new warnings have been introduced.