Node creator needs to allow for sub-domains

[liamhuber]

Now that we have the atomistics node package, the need arises for depth in our creator domains.

Currently we have

from pyiron_workflow import Workflow

Workflow.register("calculator", "pyiron_workflow.node_library.atomistics.calculator")
Workflow.register("macro", "pyiron_workflow.node_library.atomistics.calculator")
Workflow.register("task", "pyiron_workflow.node_library.atomistics.calculator")

Workflow.create.calculator.Emt()
Workflow.create.macro.Phonons()
Workflow.create.task.Bulk()

What I want is

from pyiron_workflow import Workflow

Workflow.register("atomistics", "pyiron_workflow.node_library.atomistics")

Workflow.create.atomistics.calculator.Emt()
Workflow.create.atomistics.macro.Phonons()
Workflow.create.atomistics.task.Bulk()