This PR refactors the EnsureFrontendRequestsAreStateful middleware to improve its structure and adhere more closely to the Single Responsibility Principle.

Description

The EnsureFrontendRequestsAreStateful middleware was previously responsible for two distinct tasks:

1. Determining if a request originated from a stateful frontend domain.
2. Applying the appropriate middleware pipeline based on that determination.

This refactor extracts the domain-checking logic into its own dedicated class, FrontendRequestChecker. This simplifies the middleware, making its sole responsibility to orchestrate the middleware pipeline.

Changes Made

• New Class: Added a new Laravel\Sanctum\Http\Middleware\FrontendRequestChecker class.
• Logic Extraction: Moved the logic for parsing referer/origin headers and comparing them against the stateful configuration from EnsureFrontendRequestsAreStateful::fromFrontend() to the new FrontendRequestChecker::isFromFrontend() method.
• Middleware Simplification: The EnsureFrontendRequestsAreStateful middleware now calls the new checker class. Its internal static method fromFrontend() has been removed.

Benefits of this Change

• Improved Readability: Each class now has a clear and focused purpose.
• Single Responsibility Principle: The middleware is no longer concerned with the implementation details of how a request is identified as coming from the frontend.
• Enhanced Testability: The FrontendRequestChecker can now be unit-tested in complete isolation, leading to simpler and more robust tests.