Release v2.0.0 - HTTP validation, i18n, and namespace change

This major release introduces a new namespace, a full internationalization system, and powerful features for validating HTTP requests, headers, and forms.

BREAKING CHANGE: The root namespace has been changed from PhpDevCommunity\RequestKit to Depo\RequestKit. All use statements in projects using this library must be updated.

Features:

HTTP Request Handling:

• withHeaders(): A new method in AbstractSchema to define validation rules for incoming HTTP headers (e.g., API keys, Content-Type).
• processFormHttpRequest(): A new method in AbstractSchema to securely process form submissions.
• CSRF Protection: The processFormHttpRequest method includes optional, secure CSRF token validation to prevent cross-site request forgery attacks.

Core Validation:

• equals(): A generic constraint has been added to AbstractType, allowing any data type to be checked for strict equality against a specific value.

Internationalization (i18n):

• A new Locale class now manages all error messages, allowing for easy translation.
• The library now ships with built-in translations for English ('en') and French ('fr').

Improvements & Fixes:

• Security: The error message for the equals() constraint no longer reveals the expected value, preventing potential secret leakage.
• Refactoring: The entire library has been moved under the Depo vendor namespace for better project identity.
• Dependency Removal: The dependency on phpdevcommunity/validator has been removed, making the library fully self-contained.
• Testing: Added comprehensive unit tests for all new features, including equals, withHeaders, processFormHttpRequest, and the Locale system.
• Documentation: The README.md has been significantly updated with examples and explanations for all new features.