feat(tpc): 禁止类型联合 T1 | T2 并优化错误提示

四类类型注解入口统一调用 RejectTypeUnion：任意 T1 | T2 直接报错，报文含行号与 CPtr[T]/rawptr[T]、const/volatile/static/export/extern 替代写法；仅保留内建修饰标记与类型的组合。

lib/Projectrans/DeclarationGenerator.py

@@ -10,7 +10,7 @@ import llvmlite.ir as ir
 from lib.core import TypeSystem
 from lib.core.TypeSystem import CTypeRegistry
 from lib.core.SymbolUtils import (
-    IsListAnnotation, AnnotationContainsName, IsCPtrSubscriptNode, IsCPtrNode,
+    IsListAnnotation, AnnotationContainsName, RejectTypeUnion, IsCPtrSubscriptNode, IsCPtrNode,
     IsRawPtrSubscriptNode, IsPtrSubscriptNode, ResolveGenericTypeArgStr,
     EnumClassIntWidth, ClassHasFuncLevelCVTable)
 
@@ -1187,6 +1187,8 @@ class DeclarationGenerator:
         if annotation is None:
             return 'i8*'
 
+        RejectTypeUnion(annotation)
+
         non_struct_types: set[str] = {'list', 'dict', 'tuple', 'set', 'array', 'CArray', 'rawarray'}
 
         if isinstance(annotation, ast.Name):