Support for Lattice types with next-nearest and next-next-nearest neighbor interactions

[zain2864]

Using the getInstance() function call to create models with the current different lattice types, there is no support for next-nearest and next-next nearest neighbors interactions. For example, in the RuCl example notebook (Link), we are trying to create a model that has interactions as such:

Here we see that we cannot create a link between nodes (0,5) and (1,6) with the existing lattices defined in PyLIQTR, thus no support to create a model with a Hexagonal Lattice yet. Adding on to the issue 15 (Link), where it is important to express next nearest interactions, and also next-next nearest interactions.