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/group_duty_pin.py

@@ -15,10 +15,11 @@ from duty_teller.db.session import session_scope
 from duty_teller.i18n import get_lang, t
 from duty_teller.services.group_duty_pin_service import (
     get_duty_message_text,
+    get_message_id,
     get_next_shift_end_utc,
+    get_pin_refresh_data,
     save_pin,
     delete_pin,
-    get_message_id,
     get_all_pin_chat_ids,
 )
 
@@ -28,6 +29,14 @@ JOB_NAME_PREFIX = "duty_pin_"
 RETRY_WHEN_NO_DUTY_MINUTES = 15
 
 
+def _sync_get_pin_refresh_data(
+    chat_id: int, lang: str = "en"
+) -> tuple[int | None, str, datetime | None]:
+    """Get message_id, duty text, next_shift_end in one DB session."""
+    with session_scope(config.DATABASE_URL) as session:
+        return get_pin_refresh_data(session, chat_id, config.DUTY_DISPLAY_TZ, lang)
+
+
 def _get_duty_message_text_sync(lang: str = "en") -> str:
     with session_scope(config.DATABASE_URL) as session:
         return get_duty_message_text(session, config.DUTY_DISPLAY_TZ, lang)
@@ -96,26 +105,27 @@ async def _refresh_pin_for_chat(
 ) -> Literal["updated", "no_message", "failed"]:
     """Refresh pinned duty message: send new message, unpin old, pin new, save new message_id.
 
+    Uses single DB session for message_id, text, next_shift_end (consolidated).
+
     Returns:
         "updated" if the message was sent, pinned and saved successfully;
         "no_message" if there is no pin record for this chat;
         "failed" if send_message or permissions failed.
     """
     loop = asyncio.get_running_loop()
-    message_id = await loop.run_in_executor(None, _sync_get_message_id, chat_id)
+    message_id, text, next_end = await loop.run_in_executor(
+        None,
+        lambda: _sync_get_pin_refresh_data(chat_id, config.DEFAULT_LANGUAGE),
+    )
     if message_id is None:
         logger.info("No pin record for chat_id=%s, skipping update", chat_id)
         return "no_message"
-    text = await loop.run_in_executor(
-        None, lambda: _get_duty_message_text_sync(config.DEFAULT_LANGUAGE)
-    )
     try:
         msg = await context.bot.send_message(chat_id=chat_id, text=text)
     except (BadRequest, Forbidden) as e:
         logger.warning(
             "Failed to send duty message for pin refresh chat_id=%s: %s", chat_id, e
         )
-        next_end = await loop.run_in_executor(None, _get_next_shift_end_sync)
         await _schedule_next_update(context.application, chat_id, next_end)
         return "failed"
     try:
@@ -127,11 +137,9 @@ async def _refresh_pin_for_chat(
         )
     except (BadRequest, Forbidden) as e:
         logger.warning("Unpin or pin after refresh failed chat_id=%s: %s", chat_id, e)
-        next_end = await loop.run_in_executor(None, _get_next_shift_end_sync)
         await _schedule_next_update(context.application, chat_id, next_end)
         return "failed"
     await loop.run_in_executor(None, _sync_save_pin, chat_id, msg.message_id)
-    next_end = await loop.run_in_executor(None, _get_next_shift_end_sync)
     await _schedule_next_update(context.application, chat_id, next_end)
     return "updated"