Add typing to all calls to ``self.stats`` (#4973)

* Add typing to all calls to ``self.stats``

All checkers inherit from a baseclass which has a ``stats`` attribute.
This attribute has a fairly unmanageable type, but the current typing includes all variations of the attribute.
Other changes not directly related to ``self.stats`` are due to ``mypy``warnings.
This incorporate the feedback received in #4954

* Add ``CheckerStatistic`` class to ``pylint/typing``

* Guard `typing.Counter` import

Co-authored-by: Marc Mueller <30130371+cdce8p@users.noreply.github.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/pylint/checkers/base_checker.py b/pylint/checkers/base_checker.py
index 5dfd7ea78..791a3cb1e 100644
--- a/pylint/checkers/base_checker.py
+++ b/pylint/checkers/base_checker.py
@@ -24,6 +24,7 @@ from pylint.constants import _MSG_ORDER, WarningScope
 from pylint.exceptions import InvalidMessageError
 from pylint.interfaces import UNDEFINED, IRawChecker, ITokenChecker, implements
 from pylint.message.message_definition import MessageDefinition
+from pylint.typing import CheckerStats
 from pylint.utils import get_rst_section, get_rst_title
 
 
@@ -51,6 +52,7 @@ class BaseChecker(OptionsProviderMixIn):
             self.name = self.name.lower()
         OptionsProviderMixIn.__init__(self)
         self.linter = linter
+        self.stats: CheckerStats = {}
 
     def __gt__(self, other):
         """Permit to sort a list of Checker by name."""