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/tcp_server.py

@@ -0,0 +1,90 @@
+"""Async TCP server for exposing virtual instruments over network.
+
+This module provides the InstrumentServer class that hosts virtual SCPI
+instruments over TCP, allowing client applications to communicate using
+standard SCPI commands over a network connection.
+"""
+
+from __future__ import annotations
+
+import asyncio
+import logging
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from py_dvt_ate.simulation.virtual.base import BaseInstrument
+
+logger = logging.getLogger(__name__)
+
+
+class InstrumentServer:
+    """Async TCP server hosting virtual SCPI instruments.
+
+    Each instrument is assigned a port. Clients connect via TCP and send
+    SCPI commands as newline-terminated strings. Responses are also
+    newline-terminated.
+
+    Attributes:
+        host: Host address to bind to.
+    """
+
+    def __init__(self, host: str = "127.0.0.1") -> None:
+        """Initialise the instrument server.
+
+        Args:
+            host: Host address to bind to. Defaults to localhost.
+        """
+        self._host = host
+        self._instruments: dict[int, BaseInstrument] = {}
+        self._servers: list[asyncio.Server] = []
+        self._running = False
+
+    @property
+    def host(self) -> str:
+        """Get the host address."""
+        return self._host
+
+    @property
+    def is_running(self) -> bool:
+        """Check if server is currently running."""
+        return self._running
+
+    def register_instrument(self, port: int, instrument: BaseInstrument) -> None:
+        """Register an instrument to be served on a specific port.
+
+        Args:
+            port: TCP port number to serve the instrument on.
+            instrument: Virtual instrument to serve.
+
+        Raises:
+            ValueError: If port is already registered.
+            RuntimeError: If server is already running.
+        """
+        if self._running:
+            raise RuntimeError("Cannot register instruments while server is running")
+
+        if port in self._instruments:
+            raise ValueError(f"Port {port} is already registered")
+
+        self._instruments[port] = instrument
+        logger.info(
+            "Registered %s on port %d",
+            instrument.__class__.__name__,
+            port,
+        )
+
+    def get_instrument(self, port: int) -> BaseInstrument | None:
+        """Get the instrument registered on a port.
+
+        Args:
+            port: Port number to look up.
+
+        Returns:
+            Registered instrument, or None if port not registered.
+        """
+        return self._instruments.get(port)
+
+    @property
+    def registered_ports(self) -> list[int]:
+        """Get list of registered port numbers."""
+        return list(self._instruments.keys())