lfs: fix various signature mismatches for vfs subclasses

These were flagged by PyCharm.  I'm not sure why pytype doesn't catch these-
only `hgext/lfs/__init__.py` in the lfs extension is excluded from being
checked.

I'm not sure if the `*insidef` arg to `join()` was meant as an internal
convencience, because I see another class that gets flagged for the same
signature problem (to be fixed next).  But I don't feel bold enough to make this
an internal function, and provide a simplified public `join()` on the `vfs`
classes.  That can still be done later, if desired.  For now, process the
additional args and pass them along, even though there don't appear to be any
current callers that provide extra args to these classes.  We need all of the
subclasses to agree on the signature, or they won't be considered to implement
the `Vfs` protocol being developed.

While we're copy/pasting from the base class, bring the type annotations along
for the ride.

hgext/lfs/blobstore.py

@@ -15,6 +15,10 import os
 import re
 import socket
 
+from typing import (
+    Optional,
+)
+
 from mercurial.i18n import _
 from mercurial.node import hex
 
@@ -42,11 +46,11 from ..largefiles import lfutil
 
 
 class lfsvfs(vfsmod.vfs):
-    def join(self, path):
+    def join(self, path: Optional[bytes], *insidef: bytes) -> bytes:
         """split the path at first two characters, like: XX/XXXXX..."""
         if not _lfsre.match(path):
             raise error.ProgrammingError(b'unexpected lfs path: %s' % path)
-        return super(lfsvfs, self).join(path[0:2], path[2:])
+        return super(lfsvfs, self).join(path[0:2], path[2:], *insidef)
 
     def walk(self, path=None, onerror=None):
         """Yield (dirpath, [], oids) tuple for blobs under path
@@ -77,7 +81,7 class nullvfs(lfsvfs):
     def __init__(self):
         pass
 
-    def exists(self, oid):
+    def exists(self, path: Optional[bytes] = None) -> bool:
         return False
 
     def read(self, oid):
@@ -93,8 +97,8 class nullvfs(lfsvfs):
     def walk(self, path=None, onerror=None):
         return (b'', [], [])
 
-    def write(self, oid, data):
-        pass
+    def write(self, *args, **kwargs) -> int:
+        return 0
 
 
 class lfsuploadfile(httpconnectionmod.httpsendfile):