add tasks init file

sql_env/tasks/__init__.py

@@ -0,0 +1,11 @@
+from sql_env.tasks.easy import EASY_TASKS
+from sql_env.tasks.medium import MEDIUM_TASKS
+from sql_env.tasks.hard import HARD_TASKS
+
+ALL_TASKS = {
+    "easy": EASY_TASKS,
+    "medium": MEDIUM_TASKS,
+    "hard": HARD_TASKS,
+}
+
+TASK_SETS = ALL_TASKS