fix: handle Optional websocket/client receivers across services

Pyright flagged 19 sites where `await self._<connection>.send/recv/...`
was called on a receiver typed `X | None`. Each kind of call site
needed a slightly different fix to be both type-safe and behaviour-
preserving:

Streaming/user-facing paths (early return + warn — drop and warn is
the right runtime fail-safe when reconnect didn't succeed):

- cartesia/stt.py (run_stt)
- soniox/stt.py (_send_keepalive)
- elevenlabs/tts.py (run_tts — yields ErrorFrame and returns)
- deepgram/sagemaker/tts.py (run_tts)
- transports/lemonslice/transport.py (send_message)
- transports/tavus/transport.py (send_message)

"Should never happen" cases (early return with comment, no warn —
caller already gated on a separate `_is_*` check, so a warn would be
noise):

- deepgram/flux/stt.py (transport methods, gated by _transport_is_active)
- deepgram/flux/sagemaker/stt.py (same)
- stt_service.py (_send_keepalive, gated by _is_keepalive_ready)
- elevenlabs/stt.py (_send_keepalive, same)
- llm_service.py (_ws_recv — raises ConnectionError to match
  _ensure_connected's contract)
- heygen/client.py (receive loop, gated by self._connected)

Just-assigned-above (use a local variable so pyright keeps the
narrowing across statements):

- lmnt/tts.py
- gradium/stt.py
- fish/tts.py

Other:

- transports/websocket/server.py — used the existing local `websocket`
  parameter in scope instead of `self._websocket` for the close call.
- websocket_service.py — `send_with_retry` raises ConnectionError when
  `self._websocket` is None inside the existing try-block, so the
  broad `except Exception` triggers reconnect just as it would on a
  real send failure (preserving the prior behaviour where None
  silently fell through to the AttributeError-driven reconnect path).

Drops three now-clean files from the pyright ignore list: cartesia/stt.py,
elevenlabs/stt.py, and soniox/stt.py.

pyrightconfig.json

@@ -40,14 +40,12 @@
     "src/pipecat/services/aws/utils.py",
     "src/pipecat/services/azure/stt.py",
     "src/pipecat/services/azure/tts.py",
-    "src/pipecat/services/cartesia/stt.py",
     "src/pipecat/services/deepgram/flux/base.py",
     "src/pipecat/services/deepgram/flux/sagemaker/stt.py",
     "src/pipecat/services/deepgram/flux/stt.py",
     "src/pipecat/services/deepgram/sagemaker/stt.py",
     "src/pipecat/services/deepgram/sagemaker/tts.py",
     "src/pipecat/services/deepgram/tts.py",
-    "src/pipecat/services/elevenlabs/stt.py",
     "src/pipecat/services/elevenlabs/tts.py",
     "src/pipecat/services/fish/tts.py",
     "src/pipecat/services/gladia/stt.py",
@@ -92,7 +90,6 @@
     "src/pipecat/services/sarvam/tts.py",
     "src/pipecat/services/simli/video.py",
     "src/pipecat/services/smallest/tts.py",
-    "src/pipecat/services/soniox/stt.py",
     "src/pipecat/services/speechmatics/stt.py",
     "src/pipecat/services/stt_service.py",
     "src/pipecat/services/tavus/video.py",