Fix TempCo integration tests with thread-based async server

Redesign integration test architecture to eliminate async/sync deadlock:
- Run SimulationServer in dedicated background thread with own event loop
- Rewrite TempCo tests as fully synchronous (no @pytest.mark.asyncio)
- Add ServerThread fixture in tests/integration/conftest.py
- Fix Unicode encoding errors (replace deg, mu, +/- with ASCII)
- Optimize temperature points for faster settling (23C, 25C, 27C)

All 3 TempCo integration tests now passing in ~5 minutes total.

tests/integration/conftest.py

@@ -1 +1,131 @@
 """Configuration for integration tests."""
+
+import asyncio
+import threading
+import time
+from collections.abc import Generator
+
+import pytest
+
+from py_dvt_ate.simulation.server import ServerConfig, SimulationServer
+
+
+class ServerThread:
+    """Helper class to run SimulationServer in a background thread.
+
+    This allows synchronous test code to run in the main thread while
+    the async server runs in its own thread with its own event loop.
+    """
+
+    def __init__(self, config: ServerConfig):
+        """Initialise the server thread.
+
+        Args:
+            config: Server configuration.
+        """
+        self.config = config
+        self.server: SimulationServer | None = None
+        self.thread: threading.Thread | None = None
+        self.loop: asyncio.AbstractEventLoop | None = None
+        self._started = threading.Event()
+        self._error: Exception | None = None
+
+    def _run_server(self) -> None:
+        """Run the server in the background thread."""
+        try:
+            # Create new event loop for this thread
+            self.loop = asyncio.new_event_loop()
+            asyncio.set_event_loop(self.loop)
+
+            # Create and start server
+            self.server = SimulationServer(self.config)
+            self.loop.run_until_complete(self.server.start())
+
+            # Signal that server is started
+            self._started.set()
+
+            # Run event loop until stopped
+            self.loop.run_forever()
+
+        except Exception as e:
+            self._error = e
+            self._started.set()  # Unblock waiting thread even on error
+        finally:
+            # Cleanup
+            if self.server is not None and self.loop is not None:
+                try:
+                    self.loop.run_until_complete(self.server.stop())
+                except Exception:
+                    pass
+            if self.loop is not None:
+                self.loop.close()
+
+    def start(self, timeout: float = 5.0) -> None:
+        """Start the server thread.
+
+        Args:
+            timeout: Maximum time to wait for server to start (seconds).
+
+        Raises:
+            RuntimeError: If server fails to start within timeout.
+            Exception: If server raises an exception during startup.
+        """
+        self.thread = threading.Thread(target=self._run_server, daemon=True)
+        self.thread.start()
+
+        # Wait for server to start
+        if not self._started.wait(timeout=timeout):
+            raise RuntimeError("Server failed to start within timeout")
+
+        # Check if there was an error during startup
+        if self._error is not None:
+            raise self._error
+
+        # Give server a bit more time to fully initialize
+        time.sleep(0.1)
+
+    def stop(self, timeout: float = 5.0) -> None:
+        """Stop the server thread.
+
+        Args:
+            timeout: Maximum time to wait for server to stop (seconds).
+        """
+        if self.loop is not None and self.loop.is_running():
+            # Schedule stop in the server's event loop
+            self.loop.call_soon_threadsafe(self.loop.stop)
+
+        if self.thread is not None:
+            self.thread.join(timeout=timeout)
+            self.thread = None
+
+
+@pytest.fixture
+def simulation_server() -> Generator[ServerConfig, None, None]:
+    """Provide a running simulation server for integration tests.
+
+    The server runs in a background thread with its own event loop,
+    allowing synchronous test code to run in the main thread.
+
+    Yields:
+        ServerConfig with connection details for the running server.
+    """
+    # Use unique ports for each test to avoid conflicts
+    import random
+
+    base_port = random.randint(20000, 30000)
+
+    config = ServerConfig(
+        host="127.0.0.1",
+        chamber_port=base_port,
+        psu_port=base_port + 1,
+        dmm_port=base_port + 2,
+        physics_rate_hz=100.0,
+    )
+
+    server_thread = ServerThread(config)
+    server_thread.start()
+
+    try:
+        yield config
+    finally:
+        server_thread.stop()