feat: don't require parent on initializing TabViewItem

[Berrysoft]

No description provided.

[Copilot]

Pull request overview

This PR refactors the TabViewItem initialization API to no longer require a parent TabView reference during creation. Instead, tab items are created independently and the parent relationship is established when the item is inserted into a TabView.

Key changes:

• Changed TabViewItem::Init from &'a TabView to (), allowing tab items to be created without a parent reference
• Updated all platform implementations (WinUI, Win32, Qt, GTK, AppKit) to support deferred parent assignment
• Modified example code to pass () instead of &*tabview when initializing tab view items

Reviewed changes

Copilot reviewed 18 out of 18 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
winio/src/widgets/tab_view.rs	Changed TabViewItem component initialization to accept () instead of &'a TabView
winio/src/stub/ui/tab_view.rs	Updated stub implementation signature to remove parent parameter
winio/examples/widgets.rs	Updated all page initializations to pass () and removed unused sender parameter and unnecessary redraw message
winio/examples/subviews/*.rs	Updated all subview components to accept () initialization and changed parameter names from tabview to _init
winio-ui-winui/src/ui/tab_view.rs	Refactored to use RefCell<Option<>> for deferred parent assignment and added parent tracking in views vector
winio-ui-win32/src/ui/tab_view.rs	Added validation checks for duplicate insertions and implemented parent reparenting using SetParent to HWND_MESSAGE
winio-ui-qt/src/ui/tab_view.rs	Removed parent parameter from new() function
winio-ui-gtk/src/ui/tab_view.rs	Removed parent parameter from new() function
winio-ui-app-kit/src/ui/tab_view.rs	Changed to acquire MainThreadMarker directly instead of from parent

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