refactor: Inconsistent Normalizer Function Signatures

[Aditya8369]

All normalizer functions now follow consistent patterns:

• Input: Standardized { username, data } format with validation
• Output: Common fields (platform, username, rating, totalSolved, rank) + platform-specific fields
• Structure: Class-based inheritance from BaseNormalizer for maintainability

The inconsistent parameter handling and return structures have been resolved, making the codebase more robust and easier to extend for new platforms.

Changed files

Created 1 file, modified 5 files

• backend\scripts\testScrapers.js
• backend\src\services\platform.service.js
• backend\src\services\normalization\leetcode.normalizer.js
• backend\src\services\normalization\codechef.normalizer.js
• backend\src\services\normalization\codeforces.normalizer.js
• backend\src\services\normalization\common.normaliser.js

fixes #254

[Aditya8369]

@Yugenjr assign under ecwoc