Adds xcesched_push_jobarray() (sched.c), encoding one compact
(base jobid, array_size, one spec) Data.jobArray descriptor -- reusing
the JobSubmit capnp struct already added to the Data union in task 1.2
-- instead of N individually-encoded job structs. sched_job_new_fun()
branches on l->count > 1 to call it; the existing single-job path
(l->count == 1 -> xcesched_push_joblist()) is byte-for-byte unchanged.
Sends via direct xce_request()/OPCode_push/Request_body_pushmsg rather
than the existing xce_push_data_req() helper, which hard-rejects any
payload outside jobs/workers/resources/resvals and cannot carry a
single non-list descriptor. design.md corrected to record this
transport deviation for task 5.2 to follow.
New standalone sched_push_unit_test binary (registered in
meson.build): sched.c/dataex.c/egress.c were never linked into
controller_unit_test, and two existing test files there ship local
fakes of on_scheduler_join()/notify()/collect_confvars() that would
collide with the real definitions at link time.
Task 5.1 of job-array-single-wal-record (Requirements 6.1, 6.3, 6.4).
Rongsong Shen
5e7a4aa392