Feature/sdf obstacle

[griffin-norris]

Fixes #35

• Add signed distance field (SDF) collision geometry CollGeom to allow users to specify arbitrary SDF as obstacles
• Add versions of examples 07_trajopt and 06_online_planning using simple SDF as 11_trajopt_sdf and 12_online_planning_sdf, respectively.
• ^ Above also included helper functions to define spherical SDF, as well as to visualize the 0-level set of the SDF
• Minor tweaks to the gitignore (ignore venv/ and shawdowhand_urdf)

[chungmin99]

Hi -- I took a brief pass over the contribution, it's super cool + it works well!

I left some comments / requests, but I'm also happy to tackle these if you don't have the bandwidth.

[chungmin99]

This make_sphere_grid function seems generally useful -- what do you think about extending this function to make it a general constructor for SDFGrid, given a mesh (e.g., with trimesh.proximity.signed_distance?)

[griffin-norris]

Added a generic from_mesh constructor to handle this, let me know if that's what you had in mind.

[griffin-norris]

@chungmin99 thanks for the review! Will look into your comments, mostly seems to be small inconsistencies introduced by LLMs

[xueminchi]

This new feature is cool! SDF can represent almost any obstacles. The gradient is indeed an issue and depends on how the SDF is defined and designed. I'm eager to try this feature :D.

[griffin-norris]

@chungmin99 Finally found some time to address your comments. Let me know if you have any further thoughts