fix(overload): _PyiClass 补传内存池，修复 undefined name mb

类内方法的重载后缀要调用 GenApi.overload_sig_suffix(pool, ...)，但 _PyiClass 之前没有内存池参数。追加可选参数 mb 并从 _GeneratePyiFromAst 的两个调用点（模块级类、嵌套类）传下去；未传时 _PyiOverloadSuffix 返回 None，非重载路径行为不变。

App/lib/Stub/StubGen/Converter.vp

@@ -791,7 +791,7 @@ def _PyiFunction(buf: bytes, buf_size: sizet, pos: sizet, fn: ast.FunctionDef*,
 
 
 # _PyiClass - emit a class definition (fields and method stubs).
-def _PyiClass(buf: bytes, buf_size: sizet, pos: sizet, cls: ast.ClassDef*, indent_level: int) -> sizet:
+def _PyiClass(buf: bytes, buf_size: sizet, pos: sizet, cls: ast.ClassDef*, indent_level: int, mb: memhub.MemBuddy* = None) -> sizet:
     """Emit a class definition into buf and return the new pos"""
     # enum / struct / union / renum sugar: never write EnumBase / StructBase / ... bases.
     cls_header: str = "class"
@@ -970,7 +970,7 @@ def _PyiClass(buf: bytes, buf_size: sizet, pos: sizet, cls: ast.ClassDef*, inden
                 # Nested classes
                 elif sk == ast.ASTKind.ClassDef:
                     ncls: ast.ClassDef* = ast.ClassDef*(stmt)
-                    pos = _PyiClass(buf, buf_size, pos, ncls, indent_level + 1)
+                    pos = _PyiClass(buf, buf_size, pos, ncls, indent_level + 1, mb)
                     has_member = 1
             ci += 1
 
@@ -1125,7 +1125,7 @@ def _GeneratePyiFromAst(mb: memhub.MemBuddy*, tree: ast.AST*, rel_path: str, buf
             # Class definition
             elif k == ast.ASTKind.ClassDef:
                 cls: ast.ClassDef* = ast.ClassDef*(stmt)
-                pos = _PyiClass(buf, buf_size, pos, cls, 0)
+                pos = _PyiClass(buf, buf_size, pos, cls, 0, mb)
 
             # Annotated variable declaration
             elif k == ast.ASTKind.AnnAssign: