Adding lots of clips is extremely slow with auto_transitions enabled
If adding clips to a layer that has auto_transitions enabled, the per-clip adding time seems to start to grow with some exponential properties.
This test case demonstrates it with 800 clips, which takes over 6 minutes for me. 1200 clips takes over 21 minutes already for me with this code. The code where I noticed the problem is a bit different (using the file backed asset for an URIClip audio), and is actually for some reason much faster, but still in the minutes territory.