Code Refactoring: Create an interface for OCR providers

[T-Eberle]

To make sure that the code for OCR providers is more readable and its easier to add more OCR engines, I recommend adding an interface with common methods to reduce code complexity. See PR #614

Tasks:

• Creating a common validation interface for all OCR providers
• Moving validation logic from provider.go's NewProvider into individual provider implementations
• Establishing consistent patterns for future OCR provider additions