chore(test): 移除工程配置里的 -Wl,--allow-multiple-definition 兜底

该 flag 会静默吞掉真实重复符号（PYI_BUF_SIZE 一类），违背 fail-fast。逐个工程移除后由 TPV 自举产物重建并运行验证，顺序回归 77/77 全通过。顺带提交 ProbeGen 配置 project.vpj -> project.json 的重命名（回归脚本只认 project.json）。

ThreadingTest/project.json

@@ -10,7 +10,7 @@
     },
     "linker": {
         "cmd": "clang++",
-        "flags": ["-lmsvcrt", "-lucrt", "-lpthread", "-lmingwex", "-lkernel32", "-Wl,--allow-multiple-definition"],
+        "flags": ["-lmsvcrt", "-lucrt", "-lpthread", "-lmingwex", "-lkernel32"],
         "output": "ThreadingTest.exe"
     },
     "includes": [