Add some missing #include directives (#2080)

Fixes failure to compile with GCC 13.

arbor/include/arbor/morph/primitives.hpp

@@ -2,6 +2,7 @@
 
 #include <algorithm>
 #include <cstdlib>
+#include <cstdint>
 #include <ostream>
 #include <vector>
 

arbor/threading/threading.cpp

 #include <atomic>
+#include <stdexcept>
 
 #include <arbor/assert.hpp>
 #include <arbor/util/scope_exit.hpp>