feat: Add VRM Blender addon with complete import/export functionality

- Add core VRM addon infrastructure with manifest and registration
- Add common utilities module with file system, logging, and conversion helpers
- Add human bone mapper with support for multiple rigging standards (Mixamo, MMD, Unreal, Rigify, etc.)
- Add VRM 0.x and 1.x format support with property groups and handlers
- Add editor UI panels for VRM metadata, spring bones, and MToon materials
- Add exporter with glTF2 extension support for VRM format serialization
- Add importer with scene reconstruction and armature generation
- Add MToon shader support with auto-setup and material migration
- Add spring bone physics simulation with constraint handling
- Add node constraint editor for advanced rigging control
- Add comprehensive validation and error handling with user dialogs
- Add scene watcher for real-time property synchronization
- Add workspace management and preference system
- Include Python cache files and Blender manifest configuration
- This is the initial commit establishing the complete VRM addon ecosystem for Blender

common/fs.py

@@ -0,0 +1,42 @@
+# SPDX-License-Identifier: MIT OR GPL-3.0-or-later
+import sys
+from pathlib import Path
+from typing import Optional
+
+
+def create_unique_indexed_directory_path(path: Path) -> Path:
+    name = path.name
+    for count in range(sys.maxsize):
+        count_str = f".{count}" if count else ""
+        path = path.with_name(name + count_str)
+        try:
+            path.mkdir(parents=True)
+        except OSError:
+            continue
+        return path
+    message = f"Failed to create unique directory path: {path}"
+    raise RuntimeError(message)
+
+
+def create_unique_indexed_file_path(path: Path, binary: Optional[bytes] = None) -> Path:
+    suffix = path.suffix
+    stem = path.stem
+    for count in range(sys.maxsize):
+        count_str = f".{count}" if count else ""
+        path = path.with_name(stem + count_str + suffix)
+
+        if binary is None:
+            if not path.exists():
+                return path
+            continue
+
+        try:
+            path.touch(exist_ok=False)
+        except OSError:
+            continue
+
+        path.write_bytes(binary)
+        return path
+
+    message = f"Failed to create unique file path: {path}"
+    raise RuntimeError(message)