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_watchdog.py

@@ -110,6 +110,11 @@ class TestWatchdog(unittest.TestCase):
         watchdog.keepalive()
         self.assertEqual(len(device.writes), 1)
 
+        watchdog.impl._fd, fd = None, watchdog.impl._fd
+        watchdog.keepalive()
+        self.assertEqual(len(device.writes), 1)
+        watchdog.impl._fd = fd
+
         watchdog.disable()
         self.assertFalse(device.open)
         self.assertEqual(device.writes[-1], b'V')