Tell mypy to ignore import of cython module

[thopre]

Summary

Mypy complains following the import of cPerf because it cannot find the
module. This is because it is a cython module which mypy cannot inspect.
This commit tells mypy to ignore that import.

[danilaml]

LGTM

lnt/testing/profile/perf.py

 from __future__ import absolute_import
 from lnt.util import logger
 from .profile import ProfileImpl
 from .profilev1impl import ProfileV1
 
 import os
 import traceback
 
 try:
-    from . import cPerf
+    from . import cPerf  # type: ignore  # mypy cannot process Cython modules
 except Exception:
     pass
 
 
 class LinuxPerfProfile(ProfileImpl):
     def __init__(self):
         pass