Add Meshes.jl package extension for geometry translation (fixes #208)

[rainerrodrigues]

Description

This PR addresses issue #208 by adding native support for Meshes.jl via Julia's Package Extension system.

Changes Made

• Added Meshes as a weak dependency in Project.toml.
• Created ext/MeshesExt.jl to act as a translation layer.
• Overloaded MeshCat.setobject! to accept Meshes.Geometry types.
• Implemented translation methods for Meshes.Box and Meshes.Sphere to convert them into GeometryBasics equivalents.
• Added a helper function to safely strip Unitful units from the Meshes coordinate points before passing them to the visualizer.

Example Usage:

using MeshCat, Meshes
vis = Visualizer()
setobject!(vis, Meshes.Box(Meshes.Point(0.0, 0.0, 0.0), Meshes.Point(1.0, 2.0, 1.0)))