feat(cli): Add await_signal function to handle D-Bus signals

Introduce the await_signal function to monitor D-Bus signals with a
timeout. This uses GLib's MainLoop and threading to wait for signals
efficiently while respecting a specified timeout duration.

src/revpi_middleware/cli_commands/dbus_helper.py

@@ -1,6 +1,10 @@
 # SPDX-FileCopyrightText: 2025 KUNBUS GmbH
 # SPDX-License-Identifier: GPL-2.0-or-later
 """D-Bus helper functions for cli commands."""
+from threading import Thread
+from time import sleep
+
+from gi.repository import GLib
 from pydbus import SystemBus
 
 from ..dbus_middleware1 import REVPI_DBUS_BASE_PATH
@@ -34,3 +38,36 @@ def simple_call(method: str, *args, interface: str, object_path=REVPI_DBUS_BASE_
     revpi = bus.get(REVPI_DBUS_NAME, object_path)
     iface = revpi[interface]
     return getattr(iface, method)(*args)
+
+
+def await_signal(signal_name: str, timeout: int, interface: str, object_path=REVPI_DBUS_BASE_PATH):
+    detected_signal = False
+    timeout = int(timeout)
+    loop = GLib.MainLoop()
+    th_sleep = Thread()
+
+    def th_timeout():
+        sleep(timeout)
+        loop.quit()
+
+    def signal_handler(*args, **kwargs):
+        nonlocal detected_signal
+        detected_signal = True
+        loop.quit()
+
+    bus = SystemBus()
+    revpi = bus.get(REVPI_DBUS_NAME, object_path)
+    iface = revpi[interface]
+
+    setattr(iface, f"on{signal_name}", signal_handler)
+
+    if timeout > 0:
+        th_sleep = Thread(target=th_timeout, daemon=True)
+        th_sleep.start()
+
+    try:
+        loop.run()
+    except KeyboardInterrupt:
+        pass
+
+    return detected_signal