Rebecca/shadows

[beckyfeng08]

shadows for meshes and trimeshes as is

[brentyi]

Excited for shadow support!!!

[brentyi]

Some additional suggestions:

• Can we make enable_default_lights() take a cast_shadows: bool argument? https://viser.studio/main/scene_api/#viser.SceneApi.enable_default_lights
  • And then we can set castShadows for the default lights, this would simplify setup effort for basic things
• Can we make the add_grid() object also receive shadows? (this might require creating a transparent plane, perhaps with ShadowMaterial)