Plugin scheduler: sequential iterations with max runtime (#8496)

* pb: add job type max runtime setting

* plugin: default job type max runtime

* plugin: redesign scheduler loop

* admin ui: update scheduler settings

* plugin: fix scheduler loop state name

* plugin scheduler: restore backlog skip

* plugin scheduler: drop legacy detection helper

* admin api: require scheduler config body

* admin ui: preserve detection interval on save

* plugin scheduler: use job context and drain cancels

* plugin scheduler: respect detection intervals

* plugin scheduler: gate runs and drain queue

* ec test: reuse req/resp vars

* ec test: add scheduler debug logs

* Adjust scheduler idle sleep and initial run delay

* Clear pending job queue before scheduler runs

* Log next detection time in EC integration test

* Improve plugin scheduler debug logging in EC test

* Expose scheduler next detection time

* Log scheduler next detection time in EC test

* Wake scheduler on config or worker updates

* Expose scheduler sleep interval in UI

* Fix scheduler sleep save value selection

* Set scheduler idle sleep default to 613s

* Show scheduler next run time in plugin UI

---------

Co-authored-by: Copilot <copilot@github.com>

weed/admin/plugin/scheduler_config.go

@@ -0,0 +1,31 @@
+package plugin
+
+import "time"
+
+const (
+	defaultSchedulerIdleSleep = 613 * time.Second
+)
+
+type SchedulerConfig struct {
+	IdleSleepSeconds int32 `json:"idle_sleep_seconds"`
+}
+
+func DefaultSchedulerConfig() SchedulerConfig {
+	return SchedulerConfig{
+		IdleSleepSeconds: int32(defaultSchedulerIdleSleep / time.Second),
+	}
+}
+
+func normalizeSchedulerConfig(cfg SchedulerConfig) SchedulerConfig {
+	if cfg.IdleSleepSeconds <= 0 {
+		return DefaultSchedulerConfig()
+	}
+	return cfg
+}
+
+func (c SchedulerConfig) IdleSleepDuration() time.Duration {
+	if c.IdleSleepSeconds <= 0 {
+		return defaultSchedulerIdleSleep
+	}
+	return time.Duration(c.IdleSleepSeconds) * time.Second
+}