[Core][Distributed] use device group for all broadcast

[youkaichao]

A fix to #4444

That PR was originally tested on A100, and it showed some speedup.

However, later it seems to slow down on H100 and other machines. The hypothesis is that gloo performs poorly while nvlink is better in these high-end machines.

Before we find a good solution, we can just use device group for all the broadcast.

TODO:

investigate if it is possible and beneficial to only communicate cpu data, using mechanisms such as message queue.

[WoosukKwon]

@youkaichao Could you add some performance numbers on H100? I'm wondering how this affects the performance.

[youkaichao]

see https://docs.google.com/spreadsheets/d/1c9xgR0fGvm6SROfk7vrjwOZdYnKQk9oOafWK4_KgOyo/edit#gid=593626425 for reference. in particular, check the gloo and nccl part, around byte size 1k ~ 2k. That's the rough data size we broadcast twice.

[youkaichao]

close as #5399 will be better.