Avoid redundant __contains__ (#1739)

Let's try grabbing the array.json and group.json files,
and check for `*NotFoundError`, instead of using contains first.

Co-authored-by: Davis Bennett <davis.v.bennett@gmail.com>

zarr/hierarchy.py

@@ -27,6 +27,7 @@
 from zarr.errors import (
     ContainsArrayError,
     ContainsGroupError,
+    ArrayNotFoundError,
     GroupNotFoundError,
     ReadOnlyError,
 )
@@ -457,7 +458,7 @@ def __getitem__(self, item):
 
         """
         path = self._item_path(item)
-        if contains_array(self._store, path):
+        try:
             return Array(
                 self._store,
                 read_only=self._read_only,
@@ -468,7 +469,10 @@ def __getitem__(self, item):
                 zarr_version=self._version,
                 meta_array=self._meta_array,
             )
-        elif contains_group(self._store, path, explicit_only=True):
+        except ArrayNotFoundError:
+            pass
+
+        try:
             return Group(
                 self._store,
                 read_only=self._read_only,
@@ -479,7 +483,10 @@ def __getitem__(self, item):
                 zarr_version=self._version,
                 meta_array=self._meta_array,
             )
-        elif self._version == 3:
+        except GroupNotFoundError:
+            pass
+
+        if self._version == 3:
             implicit_group = meta_root + path + "/"
             # non-empty folder in the metadata path implies an implicit group
             if self._store.list_prefix(implicit_group):