Set the type of Event._attrs

This fixes a number of mypy errors.

Additionally, replace a lambda to allow for better type inference
(removes a misc mypy error).

nose2/events.py

@@ -7,6 +7,7 @@
 
 import argparse
 import logging
+import typing as t
 import unittest
 
 from nose2 import config, util
@@ -363,7 +364,7 @@ class Event:
 
     """
 
-    _attrs = ("handled",)
+    _attrs: t.ClassVar[tuple[str, ...]] = ("handled",)
     version = "0.4"
 
     def __init__(self, **metadata):

nose2/tests/unit/test_prof_plugin.py

@@ -22,7 +22,11 @@ def tearDown(self):
     def test_startTestRun_sets_executeTests(self):
         _prof = Stub()
         _prof.runcall = object()
-        prof.cProfile.Profile = lambda: _prof
+
+        def _profile_call() -> Stub:
+            return _prof
+
+        prof.cProfile.Profile = _profile_call
         event = StartTestRunEvent(
             runner=None, suite=None, result=None, startTime=None, executeTests=None
         )