interfaces: convert `repository.peer` to a Protocol class

This is similar to the transformation in 3a90a6fd710d for dirstate.  However,
`ipeerbase` isn't referenced anywhere other than the `implementer` decorator on
this class.  I suspect, based on the lack of `self` args on these classes prior
to c1674551c109, that zope enforced that interfaces and implementations are
separate entities.  `Protocol` does not, so fold the former interface definition
into the class.

Per (seemingly undocumented) pytype desire, the `Protocol` subclass comes last
in the list.

mercurial/interfaces/repository.py

@@ -399,18 +399,13 class ipeerrequests(Protocol):
         """
 
 
-class ipeerbase(_ipeerconnection, ipeercapabilities, ipeerrequests):
+class peer(_ipeerconnection, ipeercapabilities, ipeerrequests, Protocol):
     """Unified interface for peer repositories.
 
     All peer instances must conform to this interface.
     """
 
-
[e-mail](ipeerbase)
-class peer:
-    """Base class for peer repositories."""
-
-    limitedarguments = False
+    limitedarguments: bool = False
 
     def __init__(self, ui, path=None, remotehidden=False):
         self.ui = ui