feat(body_mesh): Add body mesh separator module with edge dissolution

- Add body_mesh submodule with VRM_OT_separate_non_skin_faces operator
- Add VRM_PT_body_mesh_separator panel for UI integration
- Add utility functions for mesh operations and edge dissolution logic
- Add comprehensive edge dissolution configuration files for all body parts (head, torso, arms, legs, hands) with UV coordinates
- Add test utilities for validating mesh separation operations
- Add .gitignore to exclude Python cache files and test artifacts
- Register body_mesh module in editor package initialization
- Update registration.py to include new body mesh components

editor/body_mesh/utils.py

@@ -0,0 +1,88 @@
+# SPDX-License-Identifier: MIT OR GPL-3.0-or-later
+from dataclasses import dataclass
+from typing import TYPE_CHECKING, Optional
+
+if TYPE_CHECKING:
+    from bpy.types import Mesh, Object
+
+
+@dataclass
+class MaterialInfo:
+    """材质信息数据类"""
+    name: str
+    index: int
+    face_count: int
+    is_skin: bool
+
+
+def find_body_mesh(armature: "Object") -> Optional["Object"]:
+    """
+    在Armature的子对象中查找名为"Body"的网格对象
+
+    Args:
+        armature: Armature对象
+
+    Returns:
+        Body网格对象，如果不存在则返回None
+    """
+    if armature is None:
+        return None
+
+    for child in armature.children:
+        if child.type == "MESH" and child.name == "Body":
+            return child
+
+    return None
+
+
+def is_skin_material(material_name: str) -> bool:
+    """
+    判断材质是否为皮肤材质
+
+    Args:
+        material_name: 材质名称
+
+    Returns:
+        如果材质名包含"SKIN"则返回True（不区分大小写）
+    """
+    return "SKIN" in material_name.upper()
+
+
+def get_material_face_count(mesh: "Mesh", material_index: int) -> int:
+    """
+    获取指定材质的面数量
+
+    Args:
+        mesh: 网格数据
+        material_index: 材质索引
+
+    Returns:
+        使用该材质的面数量
+    """
+    count = 0
+    for polygon in mesh.polygons:
+        if polygon.material_index == material_index:
+            count += 1
+    return count
+
+
+def generate_unique_name(base_name: str, existing_names: set[str]) -> str:
+    """
+    生成唯一的对象名称
+
+    Args:
+        base_name: 基础名称
+        existing_names: 已存在的名称集合
+
+    Returns:
+        唯一的名称
+    """
+    if base_name not in existing_names:
+        return base_name
+
+    suffix = 1
+    while True:
+        candidate = f"{base_name}.{suffix:03d}"
+        if candidate not in existing_names:
+            return candidate
+        suffix += 1