typing: make `bundlerepository` subclass `localrepository` while type checking

Currently, `mercurial/bundlerepo.py` is excluded from pytype, mostly because it
complains that various `ui` and `vfs` fields in `localrepository` are missing.
(`bundlerepository` dynamically subclasses `localrepository` when it is
instantiated, so it works at runtime.)  This makes that class hierarchy known to
pytype.

Having a protocol for `Repository` is probably the right thing to do, but that
will be a lot of work and this still reflects the class at runtime.  Subclassing
also has the benefit of making sure any method overrides have a matching
signature, so maybe this is a situation where we do both of these things.  (I'm
not sure how clear the diagnostics are if a class *almost* implements a
protocol, but is missing a method argument or similar.)  The subclassing is not
done outside of type checking runs to avoid any side effects on already complex
code.

mercurial/bundlerepo.py

@@ -16,6 +16,7 from __future__ import annotations
 import contextlib
 import os
 import shutil
+import typing
 
 from .i18n import _
 from .node import (
@@ -287,7 +288,13 def _getfilestarts(cgunpacker):
     return filespos
 
 
-class bundlerepository:
+_bundle_repo_baseclass = object
+
+if typing.TYPE_CHECKING:
+    _bundle_repo_baseclass = localrepo.localrepository
+
+
+class bundlerepository(_bundle_repo_baseclass):
     """A repository instance that is a union of a local repo and a bundle.
 
     Instances represent a read-only repository composed of a local repository