Fix occasional green artifact when using NVENC and uvc camera

[chenosaurus]

Summary

Fixes NVIDIA hardware-encoded local_video publisher corruption that showed up as green stripes or intermittent green artifacts on subscribers.

What changed

• Stop reusing the same mutable I420 frame buffer after handing frames to WebRTC.
• Copy NVENC I420 input planes independently using each plane’s actual stride instead of assuming Y/U/V are tightly packed from DataY() and StrideY().
• Applies the NVENC plane-copy fix to both H.264 and H.265 encoders.

Why

WebRTC/NVENC can consume captured frames asynchronously, so reusing the same backing buffer could overwrite frames still in flight. Separately, padded I420 buffers, such as frames prepared for local preview/display, can have UV strides that do not derive from the Y stride. The old NVENC upload path could therefore read the wrong chroma data.

[github-actions]

Changeset

The following package versions will be affected by this PR:

Package	Bump
libwebrtc	patch
livekit	patch
webrtc-sys	patch