Use dataclasses

[faretek1]

Currently, when working on scratchattach, code completion is a problem. Sometimes, misremembering the name of an attribute can cause issues - e.g. setting Session.session_id instead of Session.id. This could be partially solved/easily checked if there is good code completion available. This is the problem addressed in #381

As a solution to the code completion issue regarding many object attributes and to improved readability, using dataclasses could be a good idea. This is one of the alternatives listed in #381, and is probably the easiest and cleanest way of doing so.

Notes:

• any processing upon initialisation is to move to the __post_init__ method

• using self.__dict__.update(**entries) could be partially replaced by cls(**entries) - this will cause errors for unrecognised attribute names, which is a good thing

• These would be quite large changes so testing might be necessary

• dataclasses' built-in repr() functionality might be better for use compared to some existing __repr__ methods. However, if one is to use this, a lot of field(repr=False, ...) may be necessary

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