The CPU usage of micro-ros-agent fluctuates greatly

- Hardware description: using linux PC Ubuntu 22.04.5
- RTOS: none linux itself
- Installation type: ros2 humble setting without docker
- Version or commit hash: humble

Expected behavior
When I publish a topic with a frequency of more than 10hz, I can clearly see that the CPU usage rises from 7% to 70%, and then gradually drops back to 7%. I would like to know what causes this. The published topic is not on the micro-ros-agent node.

Start by reproducing the report with micro-ros-agent on Ubuntu 22.04.5 using ROS 2 Humble, publishing above 10 Hz, and measure the CPU pattern described. Compare whether the published topic passes through the agent; done means identifying the cause of the fluctuation and documenting a reproducible explanation or next diagnostic step.

Written by the indexing model from the issue text.