typing: add the return type hint to pycompat.rangelist()

Not bothering with the args, because there are a few overloads and only 2
callers in the codebase, one of which is a test.

mercurial/pycompat.py

@@ -149,7 +149,7 b' def maplist(f, *args):'
     return list(map(f, *args))
 
 
-def rangelist(*args):
+def rangelist(*args) -> List[int]:
     return list(range(*args))