nogil: remove -j (multiprocessing option)

in case cpython's free-threading / nogil performance proves to
be good enough that the multiprocessing option can be removed,
this is roughly how you'd do it  (not everything's been tested)

but while you'd expect this change to improve performance,
it somehow doesn't, not even measurably so

as the performance gain is negligible, the only win here is
simplifying the code, and maybe less chance of bugs in the future

as a result, this probably won't get merged anytime soon
(if at all), and would probably warrant bumping to v2

tests/util.py

@@ -170,12 +170,14 @@ class Cfg(Namespace):
         )
 
 
-class NullBroker(object):
-    def say(self, *args):
+class NullUp2k(object):
+    def hash_file(*a):
         pass
 
-    def ask(self, *args):
-        pass
+
+class NullHub(object):
+    def __init__(self):
+        self.up2k = NullUp2k()
 
 
 class VSock(object):
@@ -206,7 +208,7 @@ class VHttpSrv(object):
         self.asrv = asrv
         self.log = log
 
-        self.broker = NullBroker()
+        self.hub = NullHub()
         self.prism = None
         self.bans = {}
         self.nreq = 0