feat(tester): extend ListProblems endpoint

internal/models/problem.go

@@ -16,3 +16,12 @@ type Problem struct {
 	CreatedAt    time.Time `db:"created_at"`
 	UpdatedAt    time.Time `db:"updated_at"`
 }
+
+type ProblemListItem struct {
+	Id          int32     `db:"id"`
+	Title       string    `db:"title"`
+	MemoryLimit int32     `db:"memory_limit"`
+	TimeLimit   int32     `db:"time_limit"`
+	CreatedAt   time.Time `db:"created_at"`
+	UpdatedAt   time.Time `db:"updated_at"`
+}