usability suggestions

After having run a couple thousand rr records now, I have some new-user suggestions.

1. It would be nice to auto-pack the traces after they are generated, even if this takes an additional flag to do so.

2. the latest-trace symlink makes it a problem to do parallel runs.

I have a 48 cpu box, but I have to run rr record -h chaos runs one-at-a-time and sequentially, because otherwise they step on each others toes via that symlink, and the two parallel scripts get confused when trying to pack the latest after a run.

And I want to say: wow! rr is fantastic. I wish I discovered it earlier! rr is such an incredible force multiplier. It's already found a ton of bugs in the tsan/race detector part of the Go runtime. cf https://github.com/golang/go/issues/74019 and https://github.com/glycerine/rr_binary_for_issue74019?tab=readme-ov-file#analysis

rr record -h (chaos mode) makes Go's race detector find issues even in code I thought was race free. Fantastic!

Thank you!