test: deflake child process exec timeout tests
On Windows it might take too long for the parent to start the communication with a child process, so by the time the parent starts its own timer, the child process might have already completed running, and the parent in those tests won't have a chance time terminate these child processes after the timeout. To address this issue, raise the time for which the child is supposed to run to make sure that the parent starts its own timer before the child terminates in the tests. Also, split the test into smaller ones to reduce the overhead.