Fix list_dir prefix stripping: use removeprefix instead of lstrip

lstrip strips individual characters from the given set, not a prefix
string. This corrupted directory names when the prefix shared characters
with child names (e.g. "temp" → "emp" when prefix contained "t").

Fixes zarr-developers#3753

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: TomNicholas

src/zarr/storage/_obstore.py

@@ -260,7 +260,7 @@ async def _transform_list_dir(
     # We assume that the underlying object-store implementation correctly handles the
     # prefix, so we don't double-check that the returned results actually start with the
     # given prefix.
-    prefixes = [obj.lstrip(prefix).lstrip("/") for obj in list_result["common_prefixes"]]
+    prefixes = [obj.removeprefix(prefix).lstrip("/") for obj in list_result["common_prefixes"]]
     objects = [obj["path"].removeprefix(prefix).lstrip("/") for obj in list_result["objects"]]
     for item in prefixes + objects:
         yield item