feat: add serializable parameter

[hiro-o918]

What

• add an object parameter implementing gokart_serialize and gokart_desirialize function

Why

• currently we need to list all the parameter to a task
  • luigi.Parameters always flattend on the task
  • luigi.Config also cannot be passed as a config object
    • we need inherit it and use as flatten parameters
• make a set of parameters are portable to be passed to a task

For example

The following example shows that this feature makes passing a set of parameters among tasks

@dataclass(frozen=True)
class Config:
    foo: int
    bar: str

    def gokart_serialize(self) -> str:
        # dict is ordered in Python 3.7+
        return json.dumps(asdict(self))

    @classmethod
    def gokart_deserialize(cls, s: str) -> 'Config':
        return cls(**json.loads(s))


class FooTask(TaskOnKart):
    config: Config = SerializableParameter(object_type=Config)

    def run(self):
        self.dump(self.config)

class BarTask(TaskOnKart):
    config: Config = SerializableParameter(object_type=Config)

    def run(self):
        self.dump(self.config)

class Pipeline(TaskOnKart):
    config: Config = SerializableParameter(object_type=Config)
    def requires(self):
        return dict(foo=FooTask(config=self.config), bar=barTask(config=self.config),

[kitagry]

LGTM

[yokomotod]

@hiro-o918 lgtm!

[yokomotod]

[memo]

I thought we may want more specific Parameter for json encode/decod-able objects, then we don't need to make custom wrapper class.

... -> fine, we can make later if we really need it.

Then, the name of SerializableParameter won't conflict / make confuse ?

... -> seems fine, we can name JsonSerializableParameter or something else.

[hiro-o918]

@yokomotod
Nice comment.
As you mentioned,SerializableParameter (this PR) is a generic purpose one.
If we need more specific parameter, we can chose a detailed name.