Correctness in debug builds is important, isn't it?

That said, panic on integer overflow in debug builds is unfortunate behavior. Overflow should cause an abort, not a panic.

> make the performance tradeoff that C++ does and defines signed integer math to wrap 2’s complement

In C++, signed overflow is undefined behavior, not wraparound. This property is useful to the optimizer for things like inferring loop bounds. The optimizer has less flexibility in equivalent Rust code.