Get intersection of two mcap files, output differences and/or common messages in multiple new mcaps

[lucasw]

Feed in 2 mcaps (and later perhaps any number >= 2, but with some limitations on outputs), output statistics and new mcap files show which messages were unique to which input mcap and which were in common.

Useful immediately for debugging which messages got dropped when one mcap/bag is played and another attempts to record everything.

Upload some example files with a few thousand messages covering 10 seconds or so.

[lucasw]

The intended use case doesn't work, there's no way to make timestamps line up between publishing from a recording and receiving without a Header.

[lucasw]

Make a test mcap that has n * 1000Hz on a single topic and a topic type that has a header, then make a test to publish that mcap and record from it, and do a intersection that only works for that type- there's no reason for that to be a rust node (except to get more practice at writing rust), just do it in python (and then it could work for any type with a Header).

[lucasw]

Make an intersection that takes the hash of the message bytes- there will be a lot of same messages that are collapsed into one, but the intersection is still useful.