feat(tts-provider): Implement TtsProvider class for text-to-speech synthesis

- Introduce TtsProvider class as an abstract base class for TTS synthesis
- Add async synthesize method to handle text input and optional speech configuration

Author: arthurbrenno

agentle/tts/tts_provider.py

@@ -0,0 +1,10 @@
+import abc
+
+from agentle.tts.real_time.definitions.speech_config import SpeechConfig
+from agentle.tts.real_time.definitions.speech_result import SpeechResult
+
+
+class TtsProvider(abc.ABC):
+    async def synthesize(
+        self, text: str, config: SpeechConfig | None = None
+    ) -> SpeechResult: ...