Auto compute chunk size by default

twnet_parser/chunk_header.py

@@ -14,7 +14,7 @@ class ChunkFlags(PrettyPrint):
 class ChunkHeader(PrettyPrint):
     def __init__(self) -> None:
         self.flags: ChunkFlags = ChunkFlags()
-        self.size: Optional[int] = 0
+        self.size: Optional[int] = None
         # TODO: should seq be a optional?
         #       so it can be None for non vital packages
         #       this could turn downstream users logic errors into