feat: implement caching for duty-related data and enhance performance

- Added a TTLCache class for in-memory caching of duty-related data, improving performance by reducing database queries.
- Integrated caching into the group duty pin functionality, allowing for efficient retrieval of message text and next shift end times.
- Introduced new methods to invalidate caches when relevant data changes, ensuring data consistency.
- Created a new Alembic migration to add indexes on the duties table for improved query performance.
- Updated tests to cover the new caching behavior and ensure proper functionality.

duty_teller/handlers/commands.py

@@ -19,7 +19,7 @@ from duty_teller.db.repository import (
     ROLE_USER,
     ROLE_ADMIN,
 )
-from duty_teller.handlers.common import is_admin_async
+from duty_teller.handlers.common import invalidate_is_admin_cache, is_admin_async
 from duty_teller.i18n import get_lang, t
 from duty_teller.utils.user import build_full_name
 
@@ -230,6 +230,7 @@ async def set_role(update: Update, context: ContextTypes.DEFAULT_TYPE) -> None:
 
     ok = await asyncio.get_running_loop().run_in_executor(None, do_set_role)
     if ok:
+        invalidate_is_admin_cache(target_user.telegram_user_id)
         await update.message.reply_text(
             t(lang, "set_role.done", name=target_user.full_name, role=role_name)
         )