Ability to merge two Ribasim models in Python

[evetion]

@SouthEndMusic

This would be helpful in writing larger testmodels that don't duplicate code, but can merge smaller test models.

Could be generically implemented as follows:

• Merge method on the TableModel class, that merges the existing table with another TableModel (e.g. PumpStatic) using pandas, taking care of unique ids, after checking the schemas are the same.
• Merge method on the NodeModel class, that takes another NodeModel (e.g. Pump) class and merges with it, by calling the merge method (see above) on all its children that are tablemodels.
• Merge method on the Model class that merges with another Model. It will call the above merge method for all its children that are Nodes.

The difficulty lies in making sure the renamed node_ids are either known at the Model merge level, and used in other methods, or the renaming of the node_ids follows a fixed schema. So when the Nodes and Edges are renamed, they still are linked to things like Pumps.

[visr]

This is probably easier to implement now after #1110. Node IDs only have to be made unique per node type. We might be able to re-use some parts of #914.

[SouthEndMusic]

Closed in favor of #1297.