A conversion method of quant_state from 0.41.0's List to 0.42.0's QuantState as a class method of QuantState

[sxndqc]

Feature request

0.41.0 represents quant_state under Params4bits as a nested list with 7 elements, but in 0.42.0 this is drastically changed to a new QuantState class, and it seems some features are discarded (e.g data_type in 0.41.0), and some features are added (QuantState.code, state2 (what's its type?) ) and I'm not very sure what that means.

Motivation

Lots of local quantized model used 0.41.0's format, which makes it hard to run them on 0.42.0.

Your contribution

I still need time to figure out what state2 is (in QuantState.as_dict it seems like another nested QuantState, but how is it constructed?). Any help or guidance is appreciated on this topic!