Refactor deletion (#28610)

Introduce the new generic deletion methods
- `func DeleteByID[T any](ctx context.Context, id int64) (int64, error)`
- `func DeleteByIDs[T any](ctx context.Context, ids ...int64) error`
- `func Delete[T any](ctx context.Context, opts FindOptions) (int64,
error)`

So, we no longer need any specific deletion method and can just use
the generic ones instead.

Replacement of #28450

Closes #28450

---------

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

services/mirror/mirror_push.go

@@ -12,6 +12,7 @@ import (
 	"strings"
 	"time"
 
+	"code.gitea.io/gitea/models/db"
 	repo_model "code.gitea.io/gitea/models/repo"
 	"code.gitea.io/gitea/modules/git"
 	"code.gitea.io/gitea/modules/lfs"
@@ -93,8 +94,9 @@ func SyncPushMirror(ctx context.Context, mirrorID int64) bool {
 		log.Error("PANIC whilst syncPushMirror[%d] Panic: %v\nStacktrace: %s", mirrorID, err, log.Stack(2))
 	}()
 
-	m, err := repo_model.GetPushMirror(ctx, repo_model.PushMirrorOptions{ID: mirrorID})
-	if err != nil {
+	// TODO: Handle "!exist" better
+	m, exist, err := db.GetByID[repo_model.PushMirror](ctx, mirrorID)
+	if err != nil || !exist {
 		log.Error("GetPushMirrorByID [%d]: %v", mirrorID, err)
 		return false
 	}