* repro: make stages run in order of the graph.
In case of --single-item, this means it'll run in the order of arguments passed.
For --downstream, this fixes running of stage out of order when multiple arguments are passed.
For normal case, this enforces the same logic, so that they are never run out-of-order.
* add tests
* tests: repro: add test for --single-item with multiple targets
* graph: support when no nodes are provided