refactor: Config序列化统一BaseConfig基类

- 新增astrai/config/base.py，提供to_dict/from_dict基类
- 统一命名：load/save → from_file/to_file
- Checkpoint.meta合并训练配置到meta.json
- sys.stderr.warn → warnings.warn
- from_file改为classmethod

astrai/config/train_config.py

@@ -6,9 +6,11 @@ from torch.optim import Optimizer
 from torch.optim.lr_scheduler import LRScheduler
 from torch.utils.data import Dataset
 
+from astrai.config.base import BaseConfig
+
 
 @dataclass
-class TrainConfig:
+class TrainConfig(BaseConfig):
     # basic setting
     model: nn.Module = field(default=None, metadata={"help": "Model for training."})
     strategy: str = field(default=None, metadata={"help": "Training strategy."})