Fix typing of View classes

[gerlero]

No description provided.

[Copilot]

Pull Request Overview

This PR fixes the typing of View classes by updating them to properly inherit from the standard library's mapping view classes while maintaining their custom functionality.

• Refactored View classes to inherit from standard library view classes (KeysView, ItemsView, ValuesView) instead of custom base classes
• Updated MultiMappingView to inherit from MappingView and use Any type annotations for broader compatibility
• Corrected return type annotations for mapping view methods to align with standard library interfaces

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