setup serial to 921600 baud

[hippo5329]

For linorobot2_hardware, the serial baudrate needs to be 921600 for esp32 to support micro-ROS messages running at 50Hz. While teensy, pico and esp32-s3 do not have such issue with their build-in usb cdc protocol (ttyACM0). I have updated my repo. Please fetch and rebase/merge. The performance of esp32 (46Hz) is a bit slower than pico (50Hz), perhaps due to uart and freertos overhead. Thanks to rdxagn9x91 to find out this issue.