unchanged() ignores ZMQ reads in Python, so the read loop never exits #612

A ZMQ read in Python never updates concore.s, so unchanged() stays True even after real data comes in. A while concore.unchanged(): read(...) loop on a ZMQ port never exits.

File reads do mod.s += ins (concore_base.py line 346), but the ZMQ branch returns at line 284/286 without it. Java and C++ both update s on ZMQ reads, so it's only Python.

concore.write("out", "u", [10])          # PAIR, connected to "in"
concore.unchanged()
concore.read("in", "u", "[0]")           # [10], SUCCESS
concore.unchanged()                      # still True

Expected: False after a successful ZMQ read, same as file ports.

Tested on dev at 8e0913e, Python 3.12.10, pyzmq 27.1.0