feat: port data streams to the livekit-ffi rust implementation

Replaces the hand-rolled Python data streams (client-side header/chunk/trailer
framing over SendStreamHeader/Chunk/TrailerRequest) with the FFI's native
implementation (data streams v2: single-packet streams + deflate):

- Writers open handle-based FFI streams (text/byte_stream_open/write/close);
  chunking, stream ids, and compression now happen in rust
- send_text/send_file are one-shot FFI calls and gain a compress option
- Incoming streams arrive via text/byte_stream_opened room events; readers
  consume per-handle reader events after a read_incremental request, and
  unhandled topics dispose the owned reader handle
- New public API: StreamError (raised when a stream terminates abnormally,
  previously indistinguishable from clean EOS) and
  RoomOptions.data_stream/DataStreamOptions.max_payload_byte_length
- Drops the use_legacy_client_implementation override, so data streams v2
  support is advertised to other clients

The consumer-facing API is unchanged. Behavior changes: read errors now raise
StreamError, stream ids are rust-generated unless supplied, sender_identity is
honored consistently (was ignored for chunks/trailers), and trailers of
targeted streams are no longer broadcast room-wide.

Author: 1egoman

livekit-rtc/livekit/rtc/__init__.py

@@ -66,6 +66,7 @@
 from .room import (
     ConnectError,
     DataPacket,
+    DataStreamOptions,
     Room,
     RoomOptions,
     RtcConfiguration,
@@ -123,6 +124,7 @@
     TextStreamWriter,
     ByteStreamWriter,
     ByteStreamReader,
+    StreamError,
 )
 from .data_track import (
     LocalDataTrack,
@@ -172,6 +174,7 @@
     "ConnectError",
     "Room",
     "RoomOptions",
+    "DataStreamOptions",
     "RtcConfiguration",
     "SimulateScenarioKind",
     "SipDTMF",
@@ -217,6 +220,7 @@
     "TextStreamWriter",
     "ByteStreamReader",
     "ByteStreamWriter",
+    "StreamError",
     "AudioProcessingModule",
     "PlatformAudio",
     "PlatformAudioSource",