Fix: Default Mode In show_dash Causes TypeError

1. Fix the TypeError one encounters when using FigureResampler's
   show_dash method with the default mode, which is None.
2. Add test.

Author: yzhaoinuw

plotly_resampler/figure_resampler/figure_resampler.py

@@ -530,9 +530,9 @@ def show_dash(
         available_modes = list(dash._jupyter.JupyterDisplayMode.__args__) + [
             "inline_persistent"
         ]
-        assert (
-            mode is None or mode in available_modes
-        ), f"mode must be one of {available_modes}"
+        if mode is None:
+            mode = "external"
+        assert mode in available_modes, f"mode must be one of {available_modes}"
         graph_properties = {} if graph_properties is None else graph_properties
         assert "config" not in graph_properties  # There is a param for config
         if self["layout"]["autosize"] is True and self["layout"]["height"] is None:

tests/test_figure_resampler.py

@@ -2024,3 +2024,11 @@ def test_manual_range_def(shared_xaxes):
     assert isinstance(ud, list) and len(ud) == 2
     ud = fig._construct_update_data({"xaxis2.range": [2, 10], "xaxis.range": [5, 100]})
     assert isinstance(ud, list) and len(ud) == 3
+
+
+def test_show_dash_with_default_mode():
+    x = np.arange(100)
+    y = np.sin(x)
+    fig = FigureResampler(go.Figure())
+    fig.add_trace(go.Scattergl(), hf_x=x, hf_y=y)
+    fig.show_dash(config={"scrollZoom": True})  # mode defaults to None