As part of this, loosened up handling of exclusive commands such that downstream commands not marked as exclusive are automatically treated as such. This is to avoid breakage of anyone who is currently defining an override def run() = Task.Command{ super.run()() }, which would otherwise start failing since super.run has suddenly become exclusive. Only downstream commands are treated as such - non-command tasks are still an error - and I expect this is an uncommon enough scenario that it won't affect much

Also cleaned up the messiness in BspRunModule and tweaked bspRun to avoid the Task.Anon that would interfere with exclusivity

Fix #5208