Collate functions for automatically finding/build node information.

[lubbersnick]

Right now there are functions for finding/making different node types in different places, such as acquire_padding_encoding, batch geometry optimizers, ase setup, lammps setup. Some parts of these functionalities are really independent of those contexts and it would serve us to collect these things into place. For example, finding an energy node to use.

Relatedly we could benefit to write a parent expansion method that simply searches the current nodes for a spec, and adds that as another parent.