feat: fill scheduler controller message gaps

Wire up 6 previously-stubbed message handlers in the scheduler:
resource dataset, resval dataset, job update notify, queue update
notify, resval update notify, and job rusage notify. Remove the
unreachable pushmsg branch (vtask_entry rewrites all pushmsg to
datamsg before the handler fires).

Changes by component:
- helper.h/helper.c: add xce_notify_event_name() for symbolic log names
- scheduler.h: add 5 new xce_sched_op_t values and matching union fields
- plugin.h/plugin.c: add plugin_job_rusage_hook_t and plugin_job_rusage_update()
- schedobj.c: add sched_update_existing_queue() with NULL/-ENOENT guards
- scheduler.c: wire 5 new dequeue cases; add sched_update_existing_job()
  and static sched_op_name(); emit WARN log on handler failure
- handler.c: implement sched_handle_resources/resvals (dataset) and
  sched_handle_sched_update_{job,queue,resvals}/job_rusage (notify);
  remove dead sched_handle_jobpush/workerpush and pushmsg branch;
  update TRACE logs to use symbolic name helpers
- test.c: 5 new unit tests covering notify event names, enum values,
  and queue update NULL guard (15/15 pass)

src/scheduler/include/scheduler.h

@@ -26,7 +26,12 @@ typedef enum {
     XCE_SCHED_OP_UPDATE_CONFIG,
     XCE_SCHED_OP_UPDATE_JOB,
     XCE_SCHED_OP_JSTATE_CHANGE,
-    XCE_SCHED_OP_UPDATE_WORKER
+    XCE_SCHED_OP_UPDATE_WORKER,
+    XCE_SCHED_OP_UPDATE_QUEUE,
+    XCE_SCHED_OP_UPDATE_RESOURCES,
+    XCE_SCHED_OP_UPDATE_RESVALS_FULL,
+    XCE_SCHED_OP_UPDATE_RESVALS,
+    XCE_SCHED_OP_JOB_RUSAGE
 } xce_sched_op_t;
 
 typedef struct {
@@ -46,6 +51,23 @@ typedef struct {
             uint64_t jobid;
             uint32_t state;
         } job_state_change;
+        struct {
+            xce_queue_t* queue;
+        } queueupdate;
+        struct {
+            int              nresources;
+            xce_resource_t** resources;
+        } resourceupdate;
+        struct {
+            int            nvals;
+            xce_resval_t** vals;
+        } resvalfullupdate;
+        struct {
+            xce_resval_list_t* resvals;
+        } resvalupdate;
+        struct {
+            xce_job_rusages_t* rusages;
+        } job_rusage;
     } u;
 } xce_sched_update_request_t;
 
@@ -105,6 +127,7 @@ extern xce_sched_user_t*    sched_get_user(xce_scheduler_t*, char*);
 extern xce_sched_project_t* sched_get_project(xce_scheduler_t*, char*);
 extern int                  sched_add_job(xce_scheduler_t*, xce_sched_job_t*);
 extern int sched_add_queue(xce_scheduler_t*, xce_sched_queue_t*);
+extern int sched_update_existing_queue(xce_scheduler_t*, xce_queue_t*);
 extern int sched_add_user(xce_scheduler_t*, xce_sched_user_t*);
 extern int sched_add_worker(xce_scheduler_t*, xce_sched_worker_t*);
 extern int sched_add_project(xce_scheduler_t*, xce_sched_project_t*);