Add 'Close All' menu item based on pin count and refactor code

[Lortunate]

### Description
- Added functionality to track the pin count in the PinWindow component and conditionally display the 'Close All' menu item.
- Refactored the code to optimize its structure for readability and maintainability.
- Added support for the native macOS context menu in the PinWindow component.

### Motivation and Context
These changes improve user experience by dynamically presenting relevant menu options based on context and enhance code quality for future maintainability.

### Type of Change
- [x] New feature (non-breaking change which adds functionality)
- [x] Code refactor (non-breaking change for readability and performance)

[gemini-code-assist]

Summary of Changes

Hello @Lortunate, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances the usability and maintainability of the application's pinning feature. It introduces intelligent display logic for menu options based on the number of active pins and integrates native platform UI elements for a more cohesive user experience on macOS. Additionally, the underlying code has been restructured to be cleaner and easier to manage for future development.

Highlights

• Dynamic 'Close All' Menu Item: The 'Close All' option in the context menu for pinned windows now dynamically appears only when more than one pin is active, improving user experience by presenting relevant options based on context.
• Native macOS Context Menu Support: Implemented support for the native macOS context menu within the PinWindow component, providing a more integrated and familiar user interface for macOS users.
• Pin Count Tracking: Introduced a mechanism to track the number of active pinned windows (pin count) in the backend, enabling conditional UI elements and better management of pinned items.
• Code Refactoring: The QML code for menu actions has been refactored into a dedicated QtObject, and general code structure has been optimized for improved readability and maintainability.

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[gemini-code-assist]

Code Review

This pull request introduces a new 'Close All' menu item in the PinWindow component, which is dynamically displayed based on the number of active pins. It also refactors the context menu logic into a dedicated QtObject for improved maintainability and adds support for native macOS context menus. The pin count is now tracked in the Rust backend and exposed to QML. Overall, the changes enhance user experience and code structure.