Add a dataset

Although OpenCompass has already included most commonly used datasets, users need to follow the steps below to support a new dataset if wanted:

Add a dataset script mydataset.py to the opencompass/datasets folder. This script should include:
- The dataset and its loading method. Define a MyDataset class that implements the data loading method load as a static method. This method should return data of type datasets.Dataset. We use the Hugging Face dataset as the unified interface for datasets to avoid introducing additional logic. Here's an example:
```
import datasets
from .base import BaseDataset

class MyDataset(BaseDataset):

    @staticmethod
    def load(**kwargs) -> datasets.Dataset:
        pass
```
- (Optional) If the existing evaluators in OpenCompass do not meet your needs, you need to define a MyDatasetEvaluator class that implements the scoring method score. This method should take predictions and references as input and return the desired dictionary. Since a dataset may have multiple metrics, the method should return a dictionary containing the metrics and their corresponding scores. Here's an example:
```
from opencompass.openicl.icl_evaluator import BaseEvaluator

class MyDatasetEvaluator(BaseEvaluator):

    def score(self, predictions: List, references: List) -> dict:
        pass
```
- (Optional) If the existing postprocessors in OpenCompass do not meet your needs, you need to define the mydataset_postprocess method. This method takes an input string and returns the corresponding postprocessed result string. Here's an example:
```
def mydataset_postprocess(text: str) -> str:
    pass
```

After defining the dataset loading, data postprocessing, and evaluator methods, you need to add the following configurations to the configuration file:

from opencompass.datasets import MyDataset, MyDatasetEvaluator, mydataset_postprocess

mydataset_eval_cfg = dict(
    evaluator=dict(type=MyDatasetEvaluator),
    pred_postprocessor=dict(type=mydataset_postprocess))

mydataset_datasets = [
    dict(
        type=MyDataset,
        ...,
        reader_cfg=...,
        infer_cfg=...,
        eval_cfg=mydataset_eval_cfg)
]

Detailed dataset configuration files and other required configuration files can be referred to in the Configuration Files tutorial. For guides on launching tasks, please refer to the Quick Start tutorial.