Fix mypy error by inheriting from Iterator

src/rp2/abstract_entry_set.py

@@ -12,6 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from collections import Iterator
 from copy import copy
 from datetime import date, datetime
 from typing import Dict, List, Optional, Set
@@ -167,7 +168,7 @@ def __iter__(self) -> "EntrySetIterator":
         return EntrySetIterator(self)
 
 
-class EntrySetIterator:
+class EntrySetIterator(Iterator):
     def __init__(self, entry_set: AbstractEntrySet) -> None:
         self.__entry_set: AbstractEntrySet = entry_set
         self.__entry_set_size: int = self.__entry_set.count