ItemsRepeater Memory leak

### Describe the bug

If the ItemsRepeater scrolls the scrollbar, the memory of the item will not be released.


This issue has seriously prevented me from developing projects for six months. refer to https://github.com/microsoft/microsoft-ui-xaml/issues/9961，I have previously posted similar issues, and Microsoft should fix these serious performance problems

### Steps to reproduce the bug

use test project，Switch pages to load data

[TestApp.zip](https://github.com/user-attachments/files/19597750/TestApp.zip)

### Expected behavior

_No response_

### Screenshots

_No response_

### NuGet package version

WinUI 3 - Windows App SDK 1.7.0: 1.7.250310001

### Windows version

Windows 11 (24H2): Build 26100

### Additional context

_No response_

Start with the attached TestApp.zip and reproduce the leak by using ItemsRepeater, scrolling, and switching pages to load data. Compare memory retention on Windows App SDK 1.7.0 (1.7.250310001) and define completion as identifying and fixing the retained item memory without regressing page navigation or scrolling.

Written by the indexing model from the issue text.