HeyGen improvements.

[filipi87]

Summary

• Added support for sandbox mode in HeyGen LiveAvatar integration via is_sandbox parameter
• Added configurable video settings (encoding type and quality level) via video_settings parameter
• Changed default session mode from "CUSTOM" to "LITE" with VP8 as default encoding
• Updated examples to use sandbox mode with the official sandbox avatar

[codecov]

Codecov Report

❌ Patch coverage is 0% with 21 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/pipecat/services/heygen/api_liveavatar.py	0.00%	21 Missing ⚠️

Files with missing lines	Coverage Δ
src/pipecat/services/heygen/api_liveavatar.py	0.00% <0.00%> (ø)

... and 2 files with indirect coverage changes

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[filipi87]

I suspect that HeyGen changed their API and started sending video using H.264 instead of VP8 by default.

While this works on other platforms, it looks like the LiveKit Python SDK on macOS is unable to decode H.264, so we don’t receive any video frames in Pipecat.

We will use VP8 as the default codec, while still allowing users to switch codecs in case H.264 works on other platforns.