Make ModelicaSystem.linearize() return all values

[ondras12345]

I think it is a shame to get the x0 and u0 values from OpenModelica and throw them away without returning them to the user. Thus, I have changed ModelicaSystem.linearize() to return a dataclass with all the available information.

To avoid breaking code that relies on the old return value, I have made it possible to unpack the dataclass into (A,B,C,D), as well as to use indexes 0-3 to access the matrices.
However, there are still cases where the new return value behaves differently, e.g. if someone passed the old result straight to json.dumps().

An alternative approach would be to preserve the old return value and add a new function:

def linearize_new([...]) -> LinearizationResult:
    ...

def linearize(*args, **kwargs):
    r = linearize_new(*args, **kwargs)
    return list(r)

It is up to you to decide whether changing the return value like this is acceptable. If you decide to go with the alternative approach outlined above, I'll rework this pull request.

[arun3688]

The changes looks good