Provide more explicit docs about mutable state default values

[wwwillchen]

I think the docs before were not vocal enough about avoiding this pitfall. I'm also exploring a way of programmatically safe-guarding against mutable default values, but it's a bit tricky - see #647.

[richard-to]

I think this looks better and clearer.

I did noticed in 3.11, it says dataclass will now check if the data type is hashable when determining if an object is a mutable default value or not.

[wwwillchen]

I think this looks better and clearer.

I did noticed in 3.11, it says dataclass will now check if the data type is hashable when determining if an object is a mutable default value or not.

good to know! I think we can try to port this change into dataclass_utils