typing: add some type hints to fastannotate that have decayed in the last year

Somewhere since 10db46e128d4, `_knownopts` decayed to `set` for unknown reasons.
Also, `annotateopts.default` changed from bytes to str.  While that is correct,
I noticed that PyCharm was flagging the member fields as undefined in
`shortstr()`, so add those to keep it happy.  (There are no complaints from
pytype because that module is excluded, due to the missing reference to
`linelog.copyfrom()` that I'm not sure how to fix.)

hgext/fastannotate/commands.py

@@ -7,6 +7,9 b''
 
 
 import os
+from typing import (
+    Set,
+)
 
 from mercurial.i18n import _
 from mercurial import (
@@ -254,7 +257,7 b' def fastannotate(ui, repo, *pats, **opts'
 
 
 _newopts = set()
-_knownopts = {
+_knownopts: Set[bytes] = {
     opt[1].replace(b'-', b'_')
     for opt in (fastannotatecommandargs['options'] + commands.globalopts)
 }

hgext/fastannotate/context.py

@@ -174,12 +174,16 b' class annotateopts:'
         'followmerge': True,
     }
 
+    diffopts: mdiff.diffopts
+    followrename: bool
+    followmerge: bool
+
     def __init__(self, **opts):
         for k, v in self.defaults.items():
             setattr(self, k, opts.get(k, v))
 
     @util.propertycache
-    def shortstr(self):
+    def shortstr(self) -> bytes:
         """represent opts in a short string, suitable for a directory name"""
         result = b''
         if not self.followrename: