macOS: isolate FUSE-T auxiliary mount paths

Create a fresh private parent for each FUSE-T auxiliary mount. Elevated
parents stay root-owned and grant only the original user read/search
access, restricting access through the auxiliary mount path and preventing
caller-controlled path replacement during elevated setup.

Clear inherited ACLs and reject temporary filesystems that ignore
ownership. Remove per-mount parents on setup failure and service teardown,
while preserving legacy temporary directories and discovery behavior.

Add regression coverage for permissions, unique parent creation, rollback,
and cleanup. FUSE-T transport authentication is outside this change.

src/Driver/Fuse/FuseService.h

@@ -61,6 +61,7 @@ namespace VeraCrypt
 #if defined(TC_MACOSX) && defined(VC_MACOSX_FUSET)
 		static const char *GetShutdownPath () { return "/shutdown"; }
 		static const char *GetShutdownSocketPath () { return "/shutdown-socket"; }
+		static void RemoveAuxMountParent (const string &fuseMountPoint, int parentFd = -1);
 #endif
 		static string GetDeviceType () { return "veracrypt"; }
 		static gid_t GetGroupId () { return GroupId; }