Agent stops relaying service response messages to DDS

After some amount of time the Agent can get itself into a state where it provides services, allows them to be called, forwards the messages onto to downstream micro but does not bridge the response back to the DDS

To Reproduce
Steps to reproduce the behaviour:

1. Run agent ros2 run micro_ros_agent micro_ros_agent serial --dev /dev/ttyACM0 -v6
2. Connect an MCU which provides a service
3. Run a node on the device which hosts the agent which calls the service in a tight loop
4. You will continue to see [==>> SER <<==] messages in the agent and logs in the MCU that the service call has been requested but no more [** <> **] agent messages
5. ros2 cli service calls will also hang from this point onwards
6. Restarting the agent gets everything back to normal

Expected behaviour
Agent should always bridge mcu to DDS and never need restarting

System information (please complete the following information):

• OS: Debian 11
• ROS 2 Humble and Iron
• Version 4.0.3 on iron branch