Release Candidate: 4.0.0rc0 Dropping Python 2

[mikedh]

I'll leave this open for a little while and release no earlier than October 1 2023. If merged earlier it will be as 4.0.0rcN which will only install with pip install --pre trimesh

• Dropping Python 2.7 For 4.0.0 Release #1951
• uses ruff upgrade rules with target Python 3.7, which automatically replaces .format with f-strings as well as other syntax updates.
• changes version machinery to exclusively use a manually bumped version in pyproject.toml and __version__ is retrieved from metadata
• removes setup.py in favor of just pyproject.toml aka PEP621
  • this makes the minimum supported version Python 3.7
  • PEP621 support was added after setuptools 59.6 which is the last version for Python 3.6 as far as I can tell
• Added type hints to trimesh.Trimesh
• switches sphinx theme to furo which pip, black and many other projects have switched to as it uses a post-webpack frontend stack. fixes jQuery error when using search function at https://trimsh.org/ #2011
• applies the October 2023 deprecation, which includes removing mesh.crc, mesh.md5, in favor of hash(mesh) and mesh.identifer_md5 in favor of mesh.identifier_hash
• fixes Voxel grid scale and points not updated after transform #2033
• updates docs domain from trimsh.org -> trimesh.org and will set up a cloudflare forwarding rule for the old domain when this is merged.

Todo Blocking

• figure out trimesh.typed.NDArray and trimesh.typed.ArrayLike
  • this may require backporting from numpy.typing to support 3.7+

Todo Nonblocking

• Merge outstanding PR's
• Switch all "dict with loose bag of keys" to dataclass objects (i.e. trimesh.path.arc.arc_center)
• De-scope ray refactor and merge what we have
• Cut down README and move some stuff into docs
• if possible clean up load return types
  • trimesh.load -> trimesh.Scene
  • trimesh.load_mesh -> trimesh.Trimesh
    • will require concatenation operations
  • trimesh.load_path -> trimesh.path.Path