Add std::byte pointer scaling test

Cover record-index arithmetic from std::byte storage, reproducing #22929.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: jketema

cpp/ql/test/query-tests/Security/CWE/CWE-468/semmle/IncorrectPointerScaling/IncorrectPointerScaling.expected

@@ -1,3 +1,4 @@
 | test.cpp:50:19:50:19 | p | This pointer might have type $@ (size 8), but this pointer arithmetic is done with type int * (size 4). | test.cpp:45:11:45:11 | test.cpp:45:11:45:11 | double |
 | test.cpp:94:18:94:18 | x | This pointer might have type $@ (size 4), but this pointer arithmetic is done with type short * (size 2). | test.cpp:88:21:88:21 | test.cpp:88:21:88:21 | int |
 | test.cpp:130:27:130:29 | arr | This pointer might have type $@ (size 4), but this pointer arithmetic is done with type short * (size 2). | test.cpp:128:16:128:18 | test.cpp:128:16:128:18 | int |
+| test.cpp:161:36:161:42 | storage | This pointer might have type $@ (size 1), but this pointer arithmetic is done with type Record * (size 4). | test.cpp:158:27:158:33 | test.cpp:158:27:158:33 | byte |

cpp/ql/test/query-tests/Security/CWE/CWE-468/semmle/IncorrectPointerScaling/test.cpp

@@ -146,3 +146,17 @@ int test18(int i) {
   // BAD: the pointer arithmetic uses type char*, so the offset is not scaled by sizeof(int).
   return *(int *)(charPointer + i); // $ Alert[cpp/incorrect-pointer-scaling-char]
 }
+
+namespace std {
+enum class byte : unsigned char {};
+}
+
+struct Record {
+  int value;
+};
+
+Record* test19(std::byte* storage, unsigned long recordIndex) {
+  // GOOD [FALSE POSITIVE of IncorrectPointerScaling.ql]: this offset is a
+  // record index, not a byte offset.
+  return reinterpret_cast<Record*>(storage) + recordIndex; // $ Alert[cpp/suspicious-pointer-scaling]
+}