Refactor `RouteDispatcher` and `MiddlewareManager` to rely on PSR-4 autoloading

[armanist]

Currently, RouteDispatcher and MiddlewareManager use require_once to load classes dynamically.

This approach:

• Breaks PSR-4 autoloading.
• Prevents proper use of subfolders for controllers and middlewares.
• Can lead to brittle code and maintenance issues.

Proposed changes:

• Remove require_once from both classes.
• Construct class FQCNs dynamically using the module namespace and class name.
• Add class_exists() checks to provide clear error messages if a class is missing.