perf(actions): batch per-row queries in run, job and cancellation paths (#39723)

Several Actions code paths issued one or more queries per listed row.
They now load in batch, with unchanged output.

- API job list: tasks, steps and runners load in batch
- API run list: latest attempts and their trigger users load in batch
- Repository runs page: the jobs of all active runs load in one query
- Cancelling previous runs and replacing concurrency group entries fetch
their jobs in one query

Per call with 50 rows on SQLite, base vs head:

| Path | Queries | Time |
| --- | --- | --- |
| API job list | 254 → 6 | 12.9 → 1.9 ms |
| API run list | 305 → 207 | 11.7 → 6.2 ms |
| Runs page job loading | 100 → 1 | 6.5 → 0.47 ms |
| `CancelPreviousJobs` | 546 → 496 | ~120 ms, per-job writes dominate |

The remaining run list queries come from per-run repository conversion,
which this PR doesn't change.

---------

Co-authored-by: Zettat123 <zettat123@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>

models/actions/task_list.go

@@ -9,6 +9,7 @@ import (
 	"gitea.dev/models/db"
 	"gitea.dev/modules/container"
 	"gitea.dev/modules/timeutil"
+	"gitea.dev/modules/util"
 
 	"xorm.io/builder"
 )
@@ -41,6 +42,29 @@ func (tasks TaskList) LoadJobs(ctx context.Context) error {
 	return jobsList.LoadAttributes(ctx, true)
 }
 
+func (tasks TaskList) LoadSteps(ctx context.Context) error {
+	taskIDs := container.FilterSlice(tasks, func(task *ActionTask) (int64, bool) {
+		return task.ID, task.Steps == nil
+	})
+	if len(taskIDs) == 0 {
+		return nil
+	}
+	var steps []*ActionTaskStep
+	if err := db.GetEngine(ctx).In("task_id", taskIDs).OrderBy("task_id, `index`").Find(&steps); err != nil {
+		return err
+	}
+	stepsByTask := make(map[int64][]*ActionTaskStep, len(taskIDs))
+	for _, step := range steps {
+		stepsByTask[step.TaskID] = append(stepsByTask[step.TaskID], step)
+	}
+	for _, task := range tasks {
+		if task.Steps == nil {
+			task.Steps = util.SliceNilAsEmpty(stepsByTask[task.ID])
+		}
+	}
+	return nil
+}
+
 func (tasks TaskList) LoadAttributes(ctx context.Context) error {
 	return tasks.LoadJobs(ctx)
 }