refactor : 移除 -> None 返回值标注，拆分 FSDP 参数，新增 mmap 数据集存储

- 删除所有 def 函数 -> None 返回值类型标注
- FSDPExecutor 参数从 **kwargs 拆为显式声明，None 值自动过滤
- 新增 MmapStorage (bin) 存储后端，基于 numpy.memmap 零拷贝加载
- 新增 save_bin/load_bin/json_to_bin 工具函数
- detect_format 支持 bin 格式自动检测

astrai/dataset/__init__.py

@@ -8,11 +8,15 @@ from astrai.dataset.storage import (
     BaseStorage,
     H5Storage,
     JSONStorage,
+    MmapStorage,
     MultiSegmentFetcher,
     StorageFactory,
     detect_format,
+    json_to_bin,
+    load_bin,
     load_h5,
     load_json,
+    save_bin,
     save_h5,
     save_json,
 )
@@ -25,11 +29,15 @@ __all__ = [
     "BaseStorage",
     "H5Storage",
     "JSONStorage",
+    "MmapStorage",
     "StorageFactory",
     "detect_format",
     "save_h5",
     "load_h5",
     "save_json",
     "load_json",
+    "save_bin",
+    "load_bin",
+    "json_to_bin",
     "ResumableDistributedSampler",
 ]