Publish ros1 messages from mcap

[lucasw]

ROS Topic Re-Publisher | Select topics to be published doesn't show any topics after loading ros1 messages from an mcap (but otherwise plotting them within plotjuggler works fine), but Plotjuggler does create publishers for /tf, /tf_static, and /clock when the checkbox is checked as shown with rosnode info- but no tf or tf_static messages from the mcap get played, and clock doesn't get published either.

This was indirectly reported first in facontidavide/PlotJuggler#988

One hurdle is that mcaps from mcap convert don't store message type md5sums like rosbags do, which is maybe an oversight there, but I think the md5sum could be determined from the message definition (which is in the mcap) though I'd like to figure out how both for here and other use cases for mcap playback (from rust and python).