feat: add Smallest AI STT service integration (#4162)

Add SmallestSTTService using the Pulse WebSocket API for real-time
transcription. Includes SmallestSTTSettings dataclass, 32-language
support with resolve_language fallback, VAD-driven finalize signal,
and SMALLEST_TTFS_P99 latency constant.   

Also adds X-Source and X-Pipecat-Version headers to Smallest STT
and TTS WebSocket connections.

examples/voice/voice-smallest.py

@@ -21,9 +21,10 @@ from pipecat.processors.aggregators.llm_response_universal import (
 )
 from pipecat.runner.types import RunnerArguments
 from pipecat.runner.utils import create_transport
-from pipecat.services.deepgram.stt import DeepgramSTTService
 from pipecat.services.openai.llm import OpenAILLMService
+from pipecat.services.smallest.stt import SmallestSTTService
 from pipecat.services.smallest.tts import SmallestTTSService
+from pipecat.transcriptions.language import Language
 from pipecat.transports.base_transport import BaseTransport, TransportParams
 from pipecat.transports.daily.transport import DailyParams
 from pipecat.transports.websocket.fastapi import FastAPIWebsocketParams
@@ -50,8 +51,11 @@ transport_params = {
 async def run_bot(transport: BaseTransport, runner_args: RunnerArguments):
     logger.info(f"Starting bot")
 
-    stt = DeepgramSTTService(
-        api_key=os.getenv("DEEPGRAM_API_KEY"),
+    stt = SmallestSTTService(
+        api_key=os.getenv("SMALLEST_API_KEY"),
+        settings=SmallestSTTService.Settings(
+            language=Language.EN,
+        ),
     )
 
     tts = SmallestTTSService(