Mill prompt shows many more open tasks than the parallelism limit

[lihaoyi]

See the image below, where I ran ./mill -k integration.__.local.server with repo the config -j0.5C and 10 cores on my laptop, and I would expect 5 ongoing tasks

It's not surprising to have more than 5, because some tasks may be blocked by their child ctx.fork.async futures are running. But I wouldn't expect more than 10 (5 blocked and 5 running). Maybe our scheduling is a bit wonky and letting the blocked tasks pile up rather than clearing them promptly