refactor: 删除数据流中的 JSONStore

- 移除 JSONStore 及相关函数，训练框架不再依赖 tokenizer
- Store 层只保留 H5Store 和 MmapStore 两种后端

astrai/dataset/__init__.py

@@ -5,18 +5,14 @@ from astrai.dataset.dataset import (
 from astrai.dataset.sampler import ResumableDistributedSampler
 from astrai.dataset.storage import (
     H5Store,
-    JSONStore,
     MmapStore,
     Store,
     StoreFactory,
     detect_format,
-    json_to_bin,
     load_bin,
     load_h5,
-    load_json,
     save_bin,
     save_h5,
-    save_json,
 )
 
 __all__ = [
@@ -25,15 +21,11 @@ __all__ = [
     "Store",
     "StoreFactory",
     "H5Store",
-    "JSONStore",
     "MmapStore",
     "detect_format",
     "save_h5",
     "load_h5",
-    "save_json",
-    "load_json",
     "save_bin",
     "load_bin",
-    "json_to_bin",
     "ResumableDistributedSampler",
 ]