Fix invalid_connection error when probes are used with modules

[mdko]

My additions to sanity check in the modules-v3 branch erroneously say that connections between internal module wires and probes are invalid. Probes are extra-modular, meta-level entities that shouldn't affect correctness.

For example:

import pyrtl

class Foo(pyrtl.Module):
    def __init__(self):
        super().__init__()
    
    def definition(self):
        i = self.Input(1, 'i')
        o = self.Output(3, 'o')
        b = pyrtl.Register(2, 'b')
        b.next <<= i + 1
        o <<= b

f = Foo()
for w in pyrtl.working_block().wirevector_subset(cls=pyrtl.Register):
    pyrtl.probe(w)

produces

Traceback (most recent call last):
  File "probes.py", line 16, in <module>
    pyrtl.probe(w)
  File "/Users/michael/PyRTL/pyrtl/helperfuncs.py", line 56, in probe
    p <<= w  # late assigns len from w automatically
  File "/Users/michael/PyRTL/pyrtl/wire.py", line 181, in __ilshift__
    self._build(other)
  File "/Users/michael/PyRTL/pyrtl/wire.py", line 168, in _build
    working_block().add_net(net)
  File "/Users/michael/PyRTL/pyrtl/core.py", line 297, in add_net
    self.sanity_check_net(net)
  File "/Users/michael/PyRTL/pyrtl/core.py", line 919, in sanity_check_net
    fail(arg, dest, "Argument and destination must belong to same module")
  File "/Users/michael/PyRTL/pyrtl/core.py", line 883, in fail
    raise PyrtlError('Invalid connection (%s -> %s). %s for these wire types.'
pyrtl.pyrtlexceptions.PyrtlError: Invalid connection (b/2R -> (Probe-0: b)/2O). Argument and destination must belong to same module for these wire types.