add: comment above optimization

For anybody that would change this value for whatever reason, the comment makes the tradeoff clear.

litellm/proxy/proxy_server.py

@@ -5236,6 +5236,10 @@ async def moderations(
 async def _audio_speech_chunk_generator(
     _response: HttpxBinaryResponseContent,
 ) -> AsyncGenerator[bytes, None]:
+    # chunk_size has a big impact on latency, it can't be too small or too large
+    # too small: latency is high
+    # too large: latency is low, but memory usage is high
+    # 8192 is a good compromise
     _generator = await _response.aiter_bytes(chunk_size=8192)
     async for chunk in _generator:
         yield chunk