fix: do not require plotly or bokeh when holoviews is used (#2199)

Using holoviews was failing if plotly or bokeh was not installed. It has
been fixed by verifying if they are available before applying a theme
for it in HoloviewsFormatter.

marimo/_dependencies/dependencies.py

@@ -141,6 +141,7 @@ class DependencyManager:
     duckdb = Dependency("duckdb")
     pillow = Dependency("PIL")
     plotly = Dependency("plotly")
+    bokeh = Dependency("bokeh")
     pyarrow = Dependency("pyarrow")
     openai = Dependency("openai")
     matplotlib = Dependency("matplotlib")

marimo/_output/formatters/holoviews_formatters.py

@@ -58,9 +58,11 @@ def _show_chart(
     def apply_theme(self, theme: Theme) -> None:
         import holoviews as hv  # type: ignore
 
-        hv.renderer("bokeh").theme = (
-            "dark_minimal" if theme == "dark" else None
-        )
-        hv.renderer("plotly").theme = (
-            "plotly_dark" if theme == "dark" else "plotly"
-        )
+        if DependencyManager.bokeh.has():
+            hv.renderer("bokeh").theme = (
+                "dark_minimal" if theme == "dark" else None
+            )
+        if DependencyManager.plotly.has():
+            hv.renderer("plotly").theme = (
+                "plotly_dark" if theme == "dark" else "plotly"
+            )