feat(dbus): Add running property to BusProvider

This property checks if the event loop is running, enhancing code
readability and convenience. It provides an easier way to monitor the
status of the loop, which may improve debugging and control flow
handling.

src/revpi_middleware/dbus_middleware1/bus_provider.py

@@ -46,3 +46,7 @@ class BusProvider(Thread):
         log.debug("enter BusProvider.stop")
         self._loop.quit()
         log.debug("leave BusProvider.stop")
+
+    @property
+    def running(self):
+        return self._loop.is_running()