Add hardware_dependent_fields to ZambaBaseModel's Config

[pjbull]

Currently, we publish configs with our official models so that it is easy for other people to use them. We do this by removing the properties that are hardware dependent (e.g., device: cuda or batch_size: 4) and resaving the files. This happens in a function that does the work for the configs that are passed:

https://github.com/drivendataorg/zamba/blob/33c1c2a20feec695139f9c6af2ce05d67ed291a0/zamba/models/publish_models.py#L15-L49

We can simplify and generalize this code by adding a hardware_dependent_fields property to the config and then a hardware_independent_dict method to the model that will serialize the config, removing all the hardware_dependent_fields on that model and any children that inherit from the same base model. Here's a working implementation with a small example config:

from pydantic import BaseModel

class CustomBase(BaseModel):
    class Config:
        hardware_dependent = []

    def dict_hardware_independent(self):
        full_dict = self.dict()

        # remove hardware dependent fields on children
        for field_name, field_type in self.__fields__.items():
            field_value = getattr(self, field_name, None)
            if isinstance(field_value, CustomBase):
                full_dict[field_name] = field_value.dict_hardware_independent()

        # remove hardware dependent fields on this model
        for f in self.Config.hardware_dependent:
            full_dict.pop(f)

        return full_dict

class SubModelC(CustomBase):
    x: str

    class Config:
        hardware_dependent = ['x']

class SubModelA(CustomBase):
    a: str
    b: str
    c: SubModelC

    class Config:
        hardware_dependent = ['a']

instance_a = SubModelA(a="a", b="b", c=SubModelC(x='x'))

instance_a.dict_hardware_independent()
# > {'b': 'b', 'c': {}}