Rewrite MPS parsing to use dataclasses instead of dicts

[MBradbury]

In the spirit of breaking out changes from #807, this PR includes rewriting parsing MPS files to use dataclasses instead of dicts.

This change does not add any new capabilities, and was done to:

1. Make it easier to type check the MPS parsing
2. To produce a more structured output from MPS parsing

As raised in #807, a downside is that this adds a dependency on dacite, whereas there were not previously any (depending on which backend is in use).

[pchtsp]

how to you feel about using TypedDicts instead of dataclasses? This way we keep dictionaries and still have type checking without needing extra dependencies.

[MBradbury]

I think dataclasses are the better approach.

Three other options:

1. Do not support converting from a dict back to an LpProblem (expect users to go via an MPS file)
2. Expect users to pickle the dataclasses (not human-readable)
3. Roll something equivalent to dacite.from_dict (All dacite does is provide this function, so not sure this would be sensible)

[pchtsp]

Understood. Let's just add the dacite dependency as you propose. Thanks,

[MBradbury]

I'm taking a look at how much extra code it might be to implement converting dicts to a dataclass:

@dataclass
class MPSParameters:
    name: str
    sense: int
    status: int
    sol_status: int

    @classmethod
    def fromDict(cls, data: dict[str, Any]) -> MPSParameters:
        return cls(data["name"], data["sense"], data["status"], data["sol_status"])

Each of the MPS dataclasses will just need to manually parse the dict.

[pchtsp]

Thanks for this, it's looking very good. I see that you added some from_dict and fromDict to cover the previous methods in some cases. But I think that many classes have lost them. Can you check and add the (now useless) fromDict, from_dict, toDict and to_dict. Ideally, with some kind of deprecation warning? So that we can take them out in a next version.

For example, LpVariable is missing from_dict and fromDict methods. LpProblem is missing to_dict and from_dict.

Others are missing more.

I hate to being picky about this but I already had issues removing an undocumented alias I had for a method and someone, somewhere came back to complain I did not add a deprecation warning before removing it.

[pchtsp]

I think we're missing the fromDict methods somewhere. Just for deprecation reasons, even if they're not useful anymore in pulp.

[MBradbury]

Do you want all fromDict / toDict methods marked as deprecated or just from_dict / to_dict?

[pchtsp]

I think the fromDict and toDict should stay without the deprecation warning as I would see them being part of the API, even if not very well documented.

Thanks again.
Also, feel free to add your name to the AUTHORS file as I see you're contributing regularly.

[pchtsp]

a typo in a warning. Besides that I think it's ready to merge. Right?

[pchtsp]

I think here it should say: "... use LpAffineExpression.toDict instead"

[MBradbury]

Fixed.

[MBradbury]

Yes, I think all good to merge.