feat: Add Bioxel asset catalog and layer management functionality

- Introduced a new asset catalog definition file for Blender to manage Bioxel assets.
- Implemented layer caching and snapshot functionality in `layer.py`, allowing for VDB file generation and low-resolution snapshots.
- Created node management functions in `node.py` for handling Bioxel nodes within Blender's Geometry Node Editor.
- Added an operator to extract mesh data from selected nodes in `structure.py`.
- Developed UI panels in `panels.py` for layer management, including import options and layer library display.

.gitignore

@@ -125,14 +125,14 @@ dmypy.json
 
 pythonlib*
 
-*.blend1
-
-blendcache_*
-
 *.ipynb
 
 .secrets
-
 .vdb
 
-!scipy_ndimage/*/**
+!scipy_ndimage/*/**
+
+# Blender
+*.blend1
+blendcache_*
+*.cats.txt~