Update Gradium endpoints to region-neutral URLs

Drop the EU-region default from the STT/TTS WebSocket URLs in favor of
the generic api.gradium.ai endpoint, and remove the explicit overrides
from the examples so they pick up the new defaults.

examples/transcription/transcription-gradium.py

@@ -51,7 +51,6 @@ async def run_bot(transport: BaseTransport, runner_args: RunnerArguments):
 
     stt = GradiumSTTService(
         api_key=os.environ["GRADIUM_API_KEY"],
-        api_endpoint_base_url="wss://us.api.gradium.ai/api/speech/asr",
         settings=GradiumSTTService.Settings(
             language=Language.EN,
             delay_in_frames=8,

examples/update-settings/stt/stt-gradium.py

@@ -50,10 +50,7 @@ transport_params = {
 async def run_bot(transport: BaseTransport, runner_args: RunnerArguments):
     logger.info(f"Starting bot")
 
-    stt = GradiumSTTService(
-        api_key=os.environ["GRADIUM_API_KEY"],
-        api_endpoint_base_url="wss://us.api.gradium.ai/api/speech/asr",
-    )
+    stt = GradiumSTTService(api_key=os.environ["GRADIUM_API_KEY"])
 
     tts = CartesiaTTSService(
         api_key=os.environ["CARTESIA_API_KEY"],

examples/update-settings/tts/tts-gradium.py

@@ -55,7 +55,6 @@ async def run_bot(transport: BaseTransport, runner_args: RunnerArguments):
     tts = GradiumTTSService(
         api_key=os.environ["GRADIUM_API_KEY"],
         settings=GradiumTTSService.Settings(voice="YTpq7expH9539ERJ"),
-        url="wss://us.api.gradium.ai/api/speech/tts",
     )
 
     llm = OpenAILLMService(