(#1048) Replace Pagination With Infinite Scroll

[TheRealDeLorian]

Description Of Changes

Replace remote-source First/Back/Next/Last pagination with infinite scrolling.

• Remove the pager controls from the remote package list.
• Load the first batch of packages as before, then append more results as the user scrolls near the bottom.
• Prefetch additional batches ahead of the viewport so later icons are ready before the user reaches the end of the currently loaded list.
• Keep Chocolatey search and package mapping off the UI thread, and add tiles in small chunks, so scrolling stays responsive while more packages load.
• Show a simple loaded / total status in place of the old page indicator.
• Add unit tests covering prefetch, append, end-of-list, and reset-on-reload behavior.

Local "This PC" packages were already unpaged and are unchanged.

Motivation and Context

Previously remote package results used First/Back/Next/Last paging, so users had to step through pages to find software.

Issue #1048 originally asked for a configurable page size. Discussion on that issue preferred dropping pagination entirely in favor of infinite scrolling, which matches how most app stores and package manager UIs work.

This change replaces page navigation with a continuous list that loads more packages as the user scrolls, prefetching ahead so later batches are ready before the bottom of the list is reached.

Related: #1090

Testing

1. Unit tests: RemoteSourceViewModelTests (7 passing), covering prefetch of two additional pages, append without clearing, short last batch / no further fetch, and reset after append.
2. Manual GUI testing against community and other remote sources: scroll past the first loaded batch and confirm more packages appear without using pager buttons.
3. Manual checks that search, sort, prerelease, all-versions, and refresh reset the list and start over from the top.
4. Manual checks in both tile and list views, including that scrolling remains usable while later batches load in the background.
5. Manual check of a small source that fits on one screen (no unnecessary extra fetch loop).

Operating Systems Testing

• Windows 11

Change Types Made

• Bug fix (non-breaking change).
• Feature / Enhancement (non-breaking change).
• Breaking change (fix or feature that could cause existing functionality to change).
• Documentation changes.
• PowerShell code changes.

Change Checklist

• Requires a change to the documentation.
• Documentation has been updated.
• Tests to cover my changes, have been added.
• All new and existing tests passed?
• PowerShell code changes: PowerShell v3 compatibility checked?
• All items are complete on the Definition of Done.

Related Issue

Fixes #1048