feat: add initial support for positioning

Signed-off-by: Konstantin Fickel <mail@konstantinfickel.de>

src/streamer/parse/shard.py

@@ -1,5 +1,4 @@
 from __future__ import annotations
-from typing import Optional
 from pydantic import BaseModel
 
 
@@ -13,7 +12,7 @@ class Shard(BaseModel):
 
 class StreamFile(BaseModel):
     filename: str
-    shard: Optional[Shard] = None
+    shard: Shard = None
 
 
 __all__ = ["Shard", "StreamFile"]