feat: add Aadhaar number validation utility

[sametday]

Description

This PR introduces the AadhaarValidator utility class to validate Indian Aadhaar numbers based on the standard 12-digit requirement format.

Fixes #66

Changes Made

• Added a new aadhaar_validator.dart file inside the lib/utils/ directory.
• Implemented static method isValid(String? aadhaarNumber).
• Added regex validation to ensure the number is exactly 12 digits long and does not start with 0 or 1.
• Handled empty/null inputs and stripped spaces/hyphens for accurate validation.

Type of Contribution

• Bug fix
• New feature
• Documentation update
• Refactoring

[sametday]

.

[sametday]

@deepak-dhwani

[bhushan-barbuddhe]

Hi @sametday
Thank you for your contribution. However, this appears to be a very basic validation check.

Could you please enhance this by creating a reusable utility that performs Aadhaar number validation using Veroff? This would make the validation more robust and reusable across different modules.