Add TCP server integration tests

Test connection handling, multiple clients, instrument access across
all three virtual instruments, physics engine integration, and error
handling. Update pytest-asyncio config for v1.x compatibility.

tests/integration/conftest.py

@@ -0,0 +1,11 @@
+"""Configuration for integration tests."""
+
+import pytest
+
+# Configure pytest-asyncio mode
+pytest_plugins = ("pytest_asyncio",)
+
+
+def pytest_configure(config: pytest.Config) -> None:
+    """Configure pytest for async tests."""
+    config.addinivalue_line("markers", "asyncio: mark test as async")