Handle string indexes with no meta

These changes let `SessionTotalsArray.build_from_encoded_data` handle the creation of `SessionTotalsArray` from encoded data that has no "meta" info and the indexes of the sessions are strings (as it happens when you pull them from storage).

These changes address https://codecov.sentry.io/issues/4326038619/?project=5215654&query=is%3Aunresolved&referrer=issue-stream&stream_index=0

shared/reports/types.py

@@ -223,7 +223,7 @@ def build_from_encoded_data(cls, sessions_array: Union[dict, list]):
                     extra=dict(sessions_array=sessions_array),
                 )
                 sessions_array["meta"] = {
-                    "session_count": max(sessions_array.keys()) + 1
+                    "session_count": int(max(sessions_array.keys())) + 1
                 }
             meta_info = sessions_array.pop("meta")
             session_count = meta_info["session_count"]

tests/unit/reports/test_types.py

@@ -194,6 +194,9 @@ class TestSessionTotalsArray(object):
         "meta": {"session_count": 5},
         "4": [0, 35, 35, 0, 0, "100", 5, 0, 0, 0, 0, 0, 0],
     }
+    encoded_obj_string_no_meta = {
+        "4": [0, 35, 35, 0, 0, "100", 5, 0, 0, 0, 0, 0, 0],
+    }
 
     def test_decode_session_totals_array_from_legacy(self):
         expected = SessionTotalsArray(
@@ -230,6 +233,16 @@ def test_decode_session_totals_array_string_indexes(self):
         assert expected.session_count == result.session_count
         assert expected.non_null_items == result.non_null_items
 
+    def test_decode_session_totals_array_string_indexes_no_meta(self):
+        encoded_obj_copy = deepcopy(self.encoded_obj_string_no_meta)
+        expected = SessionTotalsArray(
+            session_count=5,
+            non_null_items={4: [0, 35, 35, 0, 0, "100", 5, 0, 0, 0, 0, 0, 0]},
+        )
+        result = SessionTotalsArray.build_from_encoded_data(encoded_obj_copy)
+        assert expected.session_count == result.session_count
+        assert expected.non_null_items == result.non_null_items
+
     def test_decode_session_totals_array_no_meta(self):
         encoded_obj_copy = deepcopy(self.encoded_obj)
         encoded_obj_copy.pop("meta")