feat(TPC): 实现 isinstance 内建 + 多继承 this_adjust 字节偏移修复

isinstance 沿 class_parents 反向 BFS 收集目标类全部子类 vtable，运行时比较对象头部 vtable 指针，修复"目标是实际类祖先"场景误判；this_adjust 改用字节偏移（字段在子类与父类自身布局的字节差）修正第二父类方法体内二次 GEP 越界读。新增 Test/IsinstanceTest 覆盖 5 大场景 14 断言。

Test/IsinstanceTest/project.json

@@ -0,0 +1,29 @@
+{
+    "$schema": "https://raw.githubusercontent.com/TermiNexus/TransPyC/main/schemas/project-schema.json",
+    "name": "IsinstanceTest",
+    "version": "1.0.0",
+    "source_dir": "./App",
+    "build_dir": "./.tpv_build",
+    "compiler": {
+        "cmd": "llc",
+        "flags": ["-filetype=obj", "-relocation-model=pic"]
+    },
+    "linker": {
+        "cmd": "clang++",
+        "flags": ["-Wl,--allow-multiple-definition", "-Wl,--unresolved-symbols=ignore-in-object-files", "-lmsvcrt", "-lucrt", "-lpthread", "-lmingwex", "-lkernel32", "-luser32", "-latomic"],
+        "output": "IsinstanceTest.exe"
+    },
+    "includes": [
+        "../../includes"
+    ],
+    "target": {
+        "triple": "x86_64-pc-windows-gnu",
+        "datalayout": "e-m:w-p270:32:32-p271:32:32-p272:64:64-f80:128-n8:16:32:64-S128"
+    },
+    "options": {
+        "slice_level": 3,
+        "sha1_slice_level": 1,
+        "target": "llvm",
+        "strict_mode": true
+    }
+}