Fix Enhance Input Validation #68

[Sachin-NK]

Related to #68

This PR enhances the API serializers by addressing multiple issues to improve data integrity, security, and error prevention:

• Email Validation: Added email checks using validate_email for user-related serializers to ensure valid email formats.
• Password Handling: The password field in UserRegisterSerializer is now set to write_only to prevent exposure in API responses.
• ModelSerializer Update: Converted UserSerializer to a ModelSerializer for better integration with the model.

These improvements help catch errors early, provide clearer error messages, and make the API more reliable.