perf: use free_sized in mpz.cpp

The performance win here is pretty negligible (and of course irrelevant with the small allocator enabled), but this is consistent with it being used elsewhere.

src/runtime/mpz.cpp

@@ -324,7 +324,7 @@ static void mpz_dealloc(void *ptr, size_t size) {
 #ifdef LEAN_SMALL_ALLOCATOR
         dealloc(ptr, size);
 #else
-        free(ptr);
+        free_sized(ptr, size);
 #endif
 }