feat: export DegradationPreference enum with MaintainFramerateAndResolution

Regenerate proto files and export the DegradationPreference enum which now
includes the new MAINTAIN_FRAMERATE_AND_RESOLUTION value from livekit-ffi 0.12.68.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: xianshijing-lk

livekit-rtc/livekit/rtc/__init__.py

@@ -30,6 +30,7 @@
     ConnectionState,
     ContinualGatheringPolicy,
     DataPacketKind,
+    DegradationPreference,
     IceServer,
     IceTransportType,
     SimulateScenarioKind,
@@ -138,6 +139,7 @@
     "ConnectionQuality",
     "ConnectionState",
     "DataPacketKind",
+    "DegradationPreference",
     "TrackPublishOptions",
     "IceTransportType",
     "ContinualGatheringPolicy",