feat(screen): improve native streaming canvas foundation

[Ran-Xing]

Summary

This draft PR introduces the first stage of the native streaming canvas migration.

Changes

• Add a streaming frame abstraction between VideoToolbox output and rendering.
• Expose decoded frames from the native scrcpy video surface while preserving the existing CGImage compatibility path.
• Prepare the rendering pipeline for future Metal-backed canvas rendering.
• Add session frame generation isolation groundwork to avoid stale frame delivery after reconnects.

Scope

This PR intentionally does not replace the current SwiftUI image rendering path yet. The migration is staged to keep existing Screens functionality stable.

Next steps

• Replace CGImage conversion with Metal/CAMetalLayer rendering.
• Complete native virtual-display session path.
• Add runtime media parameter switching.