Nebula-internal packet loss when pointcloud/packets topic are oversubscribed

[mojomex]

When there are too many subscribers on Nebula's pointcloud or packets topics, the decoder thread (on which publish() is called) cannot keep up with the incoming buffered packets and the internal mt_queue overflows. This prints errors to the console but ultimately, packets are missing in the published pointclouds.

A better solution might be to publish in parallel to multiple subscribers but we have not currently investigated if this is viable, as the publish() call is not something we can influence.