refactor: BECGuiClientMixin -> BECGuiClient

- Mixin class was only used with BECDockArea, now it is a class by itself
which represents the client object connected to the GUI server ; ".main"
is the dock area of the main window
- Enhanced "wait_for_server"
- ".selected_device" is stored in Redis, to allow server-side to know
about the auto update configuration instead of keeping it on client

tests/end-2-end/conftest.py

@@ -5,8 +5,7 @@ from contextlib import contextmanager
 import pytest
 from bec_lib.endpoints import MessageEndpoints
 
-from bec_widgets.cli.client import BECDockArea
-from bec_widgets.cli.client_utils import _start_plot_process
+from bec_widgets.cli.client_utils import BECGuiClient, _start_plot_process
 from bec_widgets.utils import BECDispatcher
 from bec_widgets.widgets.containers.figure import BECFigure
 
@@ -48,20 +47,20 @@ def rpc_server_figure(gui_id, bec_client_lib):
 
 @pytest.fixture
 def rpc_server_dock(gui_id, bec_client_lib):
-    dock_area = BECDockArea(gui_id=gui_id)
-    dock_area._auto_updates_enabled = False
+    gui = BECGuiClient(gui_id=gui_id)
+    gui._auto_updates_enabled = False
     try:
-        dock_area.start_server(wait=True)
-        yield dock_area
+        gui.start_server(wait=True)
+        yield gui.main
     finally:
-        dock_area.close()
+        gui.close()
 
 
 @pytest.fixture
 def rpc_server_dock_w_auto_updates(gui_id, bec_client_lib):
-    dock_area = BECDockArea(gui_id=gui_id)
+    gui = BECGuiClient(gui_id=gui_id)
     try:
-        dock_area.start_server(wait=True)
-        yield dock_area
+        gui.start_server(wait=True)
+        yield gui, gui.main
     finally:
-        dock_area.close()
+        gui.close()

tests/end-2-end/test_bec_dock_rpc_e2e.py

@@ -239,14 +239,15 @@ def test_auto_update(bec_client_lib, rpc_server_dock_w_auto_updates, qtbot):
     dev = client.device_manager.devices
     scans = client.scans
     queue = client.queue
-    dock = rpc_server_dock_w_auto_updates
+    gui, dock = rpc_server_dock_w_auto_updates
+    auto_updates = gui.auto_updates
 
     def get_default_figure():
-        return dock.auto_updates.get_default_figure()
+        return auto_updates.get_default_figure()
 
     plt = get_default_figure()
 
-    dock.selected_device = "bpm4i"
+    gui.selected_device = "bpm4i"
 
     status = scans.line_scan(dev.samx, -5, 5, steps=10, exp_time=0.05, relative=False)
     status.wait()
@@ -274,7 +275,7 @@ def test_auto_update(bec_client_lib, rpc_server_dock_w_auto_updates, qtbot):
     )
     status.wait()
 
-    plt = dock.auto_updates.get_default_figure()
+    plt = auto_updates.get_default_figure()
     widgets = plt.widget_list
     qtbot.waitUntil(lambda: len(plt.widget_list) > 0, timeout=5000)
     plt_data = widgets[0].get_all_data()