fix: _load raises on valid-but-non-object JSON

a store file holding valid JSON that is not an object (null/number/string/array) returned a non-dict, breaking get/set/delete/get_all. now raises ValueError, matching the documented corrupt-file contract.

Signed-off-by: disqualifier <dev@disqualifier.me>

src/aiokv/aiokv.py

@@ -100,14 +100,21 @@ class AioKV:
     async def _load(self) -> Dict[str, Any]:
         """load the store from disk, returning {} if the file is absent or empty
 
-        a truncated/corrupt file raises JSONDecodeError — surfaced to the caller
-        rather than silently masking a real corruption.
+        a truncated/corrupt file raises JSONDecodeError, and a file holding valid
+        JSON that is not an object (e.g. a bare list, number, or null) raises
+        ValueError — both surfaced to the caller rather than silently masking a
+        real corruption or returning a non-dict that breaks every other method.
         """
         if not await asyncio.to_thread(os.path.exists, self.file):
             return {}
         async with aiofiles.open(self.file, mode="r") as f:
             data = await f.read()
-        return json.loads(data) if data else {}
+        if not data:
+            return {}
+        loaded = json.loads(data)
+        if not isinstance(loaded, dict):
+            raise ValueError(f"store file {self.file} does not hold a JSON object")
+        return loaded
 
     async def _save(self, cache: Dict[str, Any]) -> None:
         """write the store atomically: temp file in the same dir, then os.replace