Use a consistent method for empty object creation process

[paulf81]

Use one process for empty object creation process

In the course of resolving the issue with mutable types as default parameters in attrs classes within FLORIS in pull request #759, @RHammond2 points out that we need to pick a consistent method for empty object creation. Currently, we are at risk that if in the future we implement type checking, we could fail tests.

@RHammond2 says:

For instances like this below, I would recommend modifying slightly to ensure the typing is valid (even if unchecked currently) to use the following paragdigm:

x: NDArrayFloat = field(init=False, factory=list, converter=floris_array_converter)

Essentially what will happen if typing is implemented, without converting to the array type, it will fail. Additionally it creates some confusion (though some already exists tbc) to create a list for an object indicated to be an array.

The only place this will cause issues is with non-float arrays, in which case I'd recommend having two variations of floris_array_converter such as float_array_converter and object_array_converter. I don't know that it needs to have floris_ at the front at this point, and might be a lingering (but dated) idea from early in the design process.