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.

src/bioxelnodes/exceptions.py

@@ -1,22 +1,6 @@
-class CancelledByUser(Exception):
-    def __init__(self):
-        message = 'Cancelled by user'
-        super().__init__(message)
-
-
-class NoContent(Exception):
-    def __init__(self, message):
-        super().__init__(message)
-        self.message = message
-
-
-class NoFound(Exception):
-    def __init__(self, message):
-        super().__init__(message)
-        self.message = message
-
-
-class Incompatible(Exception):
-    def __init__(self, message):
-        super().__init__(message)
-        self.message = message
+# This file is kept for backward compatibility
+# Custom exceptions have been replaced with built-in exceptions:
+# CancelledByUser -> CancelledError
+# NoContent -> ValueError
+# NoFound -> LookupError
+# Incompatible -> ValueError