timeout: return timed-out status after kill grace period

[can1357]

uutils timeout maps the -k/--kill-after post-timeout exit path to internal failure 125 when --preserve-status is not set. GNU reports 124 for this timed-out case, so timeout events are misclassified as utility failure.

Reproduction Steps

timeout -k 1 1 sleep 10; echo "exit=$?"
# Expected (GNU): exit=124
# Actual (uutils): exit=125

Impact

Scripts that branch on timeout status treat a normal timeout as an internal tool error. This breaks GNU-compatible timeout handling in automation and monitoring pipelines.