scheduler: time-window dispatch reason (PEND-reason #17/E11)

Add queue dispatch-window support so a queue whose window is closed
(queues.yaml dispatch_window, e.g. 19:00-08:30) is treated as
non-electable and reports PREASON_TIME_WINDOW.

- lib/window.c: new xce_timewindow_is_open() — NULL/empty always open,
  same-day and overnight (close < open) segments, day-scoped (0=every day,
  1-7=Mon..Sun).
- scheduler: make_sched_queue duplicates dispatchwindow_config onto
  xce_sched_queue_t.dispatchwindow (freed by kill_sched_queue);
  sched_queue_is_ready() checks it; sched_queue_status_reason() now takes
  the queue (was a bare status bitmask) and maps a closed window to
  PREASON_TIME_WINDOW.
- fcfs: keep the windowed-out queue skip; do NOT attach the queue-status
  reason to job->schedobj from the picker thread (bug-1521: races the
  allocator thread's MOVE_PTR(obj->reason,...) and corrupts the heap).
- tests: test_window.c (5 cases) covers no-window/daily/overnight/
  day-scoped/multi-seg; full suite 295/295 pass.

Cluster-verified: with a 09:00-17:00 window on the xce queue (currently
outside the window), fcfs reports "queue xce ... ready=0 reason=8"
(PREASON_TIME_WINDOW).

Co-Authored-By: Claude <noreply@anthropic.com>

src/lib/meson.build

@@ -152,6 +152,7 @@ libxce_test_src = ['testsuite/test.c',
                    'testsuite/test_delay.c',
                    'testsuite/test_ordq.c',
                    'testsuite/test_preason.c',
+                   'testsuite/test_window.c',
                    'testsuite/test_kvmgr.c',
                    'testsuite/test_group.c',
                    'testsuite/test_xlist.c',