Define inputs and outputs of steps/tasks as attributes instead of properties to simplify definition

[plaguss]

Description

This PR does a refactor of inputs/outputs properties of the steps to be defined in terms of attributes.

Defining a custom Step (or Task) now needs to create the inputs and outputs as attributes instead of properties.
Some classes need running some code, so making a general classmethod is not feasible (maybe I'm wrong?), for example the steps in the columns.py format need information from other attributes, or the loader classes need to fetch info from the datasets which only happen after calling .load().

Instead of simplifying the access to these variables, it just simplifies the definition by writing less lines.

• Common case:

from typing import TYPE_CHECKING
from distilabel.steps import Step, StepInput
from distilabel.steps.typing import StepColumns

if TYPE_CHECKING:
    from distilabel.steps.typing import StepOutput

class MyStep(Step):
    inputs: StepColumns = ["input_field"]
    outputs: StepColumns = ["output_field"]

    def process(self, inputs: StepInput) -> "StepOutput":
        for input in inputs:
            input["output_field"] = input["input_field"]
        yield inputs

• Attributes with dependencies (do it by defining the model_post_init):

from typing import TYPE_CHECKING
from distilabel.steps import Step, StepInput
from distilabel.steps.typing import StepColumns

if TYPE_CHECKING:
    from distilabel.steps.typing import StepOutput

class RenameColumns(Step):
    rename_mappings: Dict[str, str] = None

    def model_post_init(self, __context: Any) -> None:
        super().model_post_init(__context)
        self.outputs = list(self.rename_mappings.values())  # type: ignore

    def process(self, inputs: StepInput) -> "StepOutput":  # type: ignore
        outputs = []
        for input in inputs:
            outputs.append(
                {self.rename_mappings.get(k, k): v for k, v in input.items()}  # type: ignore
            )
        yield outputs

Closes #836

[github-actions]

Documentation for this PR has been built. You can view it at: https://distilabel.argilla.io/pr-1027/

[codspeed-hq]

CodSpeed Performance Report

Merging #1027 will not alter performance

_{Comparing input-output-classmethod (4c709ae) with develop (dc06161)}

Summary

✅ 1 untouched benchmarks