PointCloud2 support; message restamping; multithreading; Go2 example

[roym899]

This adds

• partial PointCloud2 support (assuming float and x,y,z channels),
• optional restamping of message for improved visualization in Rerun when they do not have a proper timestamp,
• multithreading, and
• new Go2 example.

Still needs some clean up and proper handling of a few things. But it generally works.

go2.mp4