Add async TCP server foundation

Create InstrumentServer class with asyncio for hosting virtual SCPI
instruments over TCP. Supports registering instruments on specific
ports with port-to-instrument mapping.

src/py_dvt_ate/simulation/__init__.py

@@ -3,3 +3,7 @@
 Provides virtual instruments backed by a coupled thermal-electrical
 physics engine. Used for development and testing without real hardware.
 """
+
+from py_dvt_ate.simulation.tcp_server import InstrumentServer
+
+__all__ = ["InstrumentServer"]