Fix: add missing header stdexcept in benchmark/multithread.hpp

[ldorau]

Description

Fix: add missing header <stdexcept> in benchmark/multithread.hpp

It fixes the following build error:

In file included from /home/runner/work/unified-memory-framework/unified-memory-framework/benchmark/multithread.cpp:10:
/home/runner/work/unified-memory-framework/unified-memory-framework/benchmark/multithread.hpp: In function ‘auto umf_bench::measure(size_t, size_t, F&&)’:
/home/runner/work/unified-memory-framework/unified-memory-framework/benchmark/multithread.hpp:42:20: error: ‘runtime_error’ is not a member of ‘std’
   42 |         throw std::runtime_error("iterations must be > 1");
      |                    ^~~~~~~~~~~~~
/home/runner/work/unified-memory-framework/unified-memory-framework/benchmark/multithread.hpp:24:1: note: ‘std::runtime_error’ is defined in header ‘<stdexcept>’; did you forget to ‘#include <stdexcept>’?
   23 | #include "multithread_helpers.hpp"
  +++ |+#include <stdexcept>
   24 | 

See: https://github.com/ldorau/unified-memory-framework/actions/runs/11323579534/job/31486568812

Checklist

• Code compiles without errors locally
• All tests pass locally
• CI workflows execute properly