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.

alembic/versions/008_duties_indexes.py

@@ -0,0 +1,44 @@
+"""Add indexes on duties table for performance.
+
+Revision ID: 008
+Revises: 007
+Create Date: 2025-02-25
+
+Indexes for get_current_duty, get_next_shift_end, get_duties, get_duties_for_user.
+"""
+
+from typing import Sequence, Union
+
+from alembic import op
+
+revision: str = "008"
+down_revision: Union[str, None] = "007"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.create_index(
+        "ix_duties_event_type_start_at",
+        "duties",
+        ["event_type", "start_at"],
+        unique=False,
+    )
+    op.create_index(
+        "ix_duties_event_type_end_at",
+        "duties",
+        ["event_type", "end_at"],
+        unique=False,
+    )
+    op.create_index(
+        "ix_duties_user_id_start_at",
+        "duties",
+        ["user_id", "start_at"],
+        unique=False,
+    )
+
+
+def downgrade() -> None:
+    op.drop_index("ix_duties_user_id_start_at", table_name="duties")
+    op.drop_index("ix_duties_event_type_end_at", table_name="duties")
+    op.drop_index("ix_duties_event_type_start_at", table_name="duties")