Add await writer.drain() after writer.write() for proper flow control

[allrob23]

Summary

This PR adds await writer.drain() after writer.write() calls to ensure proper flow control and prevent potential data loss or write buffer overflows when interacting with asyncio streams.

Rationale

According to the Python asyncio documentation, writer.write() only queues data, and it’s necessary to call await writer.drain() to ensure the data is properly written when the internal buffer is full. The drain() method blocks when the buffer is full, preventing overflows and ensuring all data is transmitted before continuing execution. Without this, there is a risk of data not being fully sent or written.

This change ensures the write buffer is correctly managed, especially in cases of high-volume or rapid write operations, maintaining stream reliability and preventing potential issues in production environments.

[alengwenus]

Thanks @allrob23 !