fix: folder endpoint returning same track for different files of the same trackhash

+ fix: chunked streaming. return instead of yield chunks

app/utils/__init__.py

@@ -14,7 +14,8 @@ def format_number(number: float) -> str:
     return locale.format_string("%d", number, grouping=True)
 
 
-
-
 def flatten(list_: Iterable[list[T]]) -> list[T]:
+    """
+    Flattens a list of lists into a single list.
+    """
     return [item for sublist in list_ for item in sublist]