experimental init: Fix Solara import by making it lazy (#2357)

In the experimental `__init__.py`, it always tries to import the "old" solara_viz module, even if it's not needed because only the cell space is used. This PR wraps that in a try block to also allow using the experimental cell space without Solara installed.

Author: EwoutH

mesa/experimental/__init__.py

@@ -2,6 +2,12 @@
 
 from mesa.experimental import cell_space
 
-from .solara_viz import JupyterViz, Slider, SolaraViz, make_text
+try:
+    from .solara_viz import JupyterViz, Slider, SolaraViz, make_text
 
-__all__ = ["cell_space", "JupyterViz", "SolaraViz", "make_text", "Slider"]
+    __all__ = ["cell_space", "JupyterViz", "Slider", "SolaraViz", "make_text"]
+except ImportError:
+    print(
+        "Could not import SolaraViz. If you need it, install with 'pip install --pre mesa[viz]'"
+    )
+    __all__ = ["cell_space"]