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/convert_any.py

@@ -0,0 +1,36 @@
+# SPDX-License-Identifier: MIT OR GPL-3.0-or-later
+"""A module provides a function to convert a variable of type Any to a concrete type.
+
+Inevitably, variables of type Any may occur, and such variables cannot be handled
+in type checkers in strict mode. Any is allowed only in the module here.
+"""
+
+import sys
+from collections.abc import Iterator
+from typing import (
+    Any,  # Any is allowed only in the module here.
+    Optional,
+)
+
+
+def to_object(  # type: ignore[explicit-any]
+    any_object: Any,  # noqa: ANN401  # Any is allowed only in the module here.
+) -> object:
+    # Interpret Unknown as object
+    # https://github.com/microsoft/pyright/issues/3650
+    if not isinstance(any_object, object):
+        if sys.version_info >= (3, 11):
+            from typing import assert_never
+
+            assert_never(any_object)
+        raise TypeError
+    return any_object
+
+
+def iterator_to_object_iterator(  # type: ignore[explicit-any]
+    any_iterator: Any,  # noqa: ANN401  # Any is allowed only in the module here.
+) -> Optional[Iterator[object]]:
+    any_iterator_without_partial_type_narrowing = any_iterator
+    if not isinstance(any_iterator, Iterator):
+        return None
+    return map(to_object, any_iterator_without_partial_type_narrowing)