Enable pyright strict mode (#2652)

- added pyrightconfig.json with typeCheckingMode=strict
- added type hints to all files except api.py
- added type stubs for dns, etcd, consul, kazoo, pysyncobj and other modules
- added type stubs for psycopg2 and urllib3 with some little fixes
- fixes most of the issues reported by pyright
- remaining issues will be addressed later, along with enabling CI linting task

tests/test_utils.py

@@ -36,7 +36,7 @@ class TestUtils(unittest.TestCase):
 
     def test_enable_keepalive(self):
         with patch('socket.SIO_KEEPALIVE_VALS', 1, create=True):
-            self.assertIsNotNone(enable_keepalive(Mock(), 10, 5))
+            self.assertIsNone(enable_keepalive(Mock(), 10, 5))
         with patch('socket.SIO_KEEPALIVE_VALS', None, create=True):
             for platform in ('linux2', 'darwin', 'other'):
                 with patch('sys.platform', platform):