Port Streams from 7.x

**Source**: Microsoft.Toolkit.Uwp.UI.Helpers (7.x)
**Destination**: CommunityToolkit.WinUI.Helpers (8.x) — not yet ported

## Description

There are several operations that apps need commonly to do against their APPX, or from the Internet that are not easy. This helper class wraps up some of the most common operations we need in multiple apps.

## Prerequisites

None identified.

## Porting Basics

- [ ] Namespace updated to `CommunityToolkit.WinUI.*`
- [ ] Code for UWP, WinUI3 and Uno Platform consolidated
- [ ] Desired MultiTargets configured
- [ ] Sample code migrated
- [ ] Concept docs migrated
- [ ] Tests migrated and passing

## Quality Evaluation

See [Porting Criteria](https://github.com/CommunityToolkit/Windows/wiki/Component-Quality-Evaluation) for detailed evaluation guidance.

- [n/a] UX: Accessibility reviewed
- [n/a] UX: Visual design reviewed
- [n/a] UX: Interaction patterns appropriate
- [ ] DX: API surface reviewed
- [ ] DX: API flexibility appropriate
- [ ] DX: Documentation updated
- [ ] MX: Breaking changes documented
- [ ] MX: Domain isolation appropriate
- [ ] MX: Test coverage adequate

## Tracking Gaps

*No gaps identified — porting work not yet started.*

## Closing

- [ ] All Porting Basics complete
- [ ] Quality Evaluation reviewed
- [ ] Gaps filed as sub-issues

---

## 7x Documentation Inventory

**Docs ported to 8x**: n/a

**Docs not in 8x**: n/a

## 7x Source Inventory

**Source already ported to 8x**: n/a

**Source not ported to 8x**: n/a

## Notes

- Not currently planned for porting. Open to community interest.
- **Archive redirect**: https://learn.microsoft.com/en-us/dotnet/communitytoolkit/windows/archive/streams

Beginnen Sie mit der archivierten Streams-Dokumentation und dem 7.x-Quellcode und verwenden Sie dann die Porting Criteria, um den fehlenden WinUI- und Uno-Umfang festzulegen. Überprüfen Sie den Namespace, das Multitargeting, die Beispiele, die Konzeptdokumentation, die API-Oberfläche und die Tests; als erledigt gilt, dass die Checklisten Porting Basics, Quality Evaluation und Closing vollständig abgeschlossen sind.

Vom Indexierungsmodell aus dem Issue-Text verfasst.