feat: add calendar subscription token functionality and ICS generation

- Introduced a new database model for calendar subscription tokens, allowing users to generate unique tokens for accessing their personal calendar.
- Implemented API endpoint to return ICS files containing only the subscribing user's duties, enhancing user experience with personalized calendar access.
- Added utility functions for generating ICS files from user duties, ensuring proper formatting and timezone handling.
- Updated command handlers to support the new calendar link feature, providing users with easy access to their personal calendar subscriptions.
- Included unit tests for the new functionality, ensuring reliability and correctness of token generation and ICS file creation.

alembic/versions/005_calendar_subscription_tokens.py

@@ -0,0 +1,46 @@
+"""Calendar subscription tokens table
+
+Revision ID: 005
+Revises: 004
+Create Date: 2025-02-19
+
+"""
+
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+revision: str = "005"
+down_revision: Union[str, None] = "004"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "calendar_subscription_tokens",
+        sa.Column("id", sa.Integer(), autoincrement=True, nullable=False),
+        sa.Column("user_id", sa.Integer(), nullable=False),
+        sa.Column("token_hash", sa.Text(), nullable=False),
+        sa.Column("created_at", sa.Text(), nullable=False),
+        sa.ForeignKeyConstraint(["user_id"], ["users.id"]),
+        sa.PrimaryKeyConstraint("id"),
+        sa.UniqueConstraint(
+            "token_hash", name="uq_calendar_subscription_tokens_token_hash"
+        ),
+    )
+    op.create_index(
+        "ix_calendar_subscription_tokens_token_hash",
+        "calendar_subscription_tokens",
+        ["token_hash"],
+        unique=True,
+    )
+
+
+def downgrade() -> None:
+    op.drop_index(
+        "ix_calendar_subscription_tokens_token_hash",
+        table_name="calendar_subscription_tokens",
+    )
+    op.drop_table("calendar_subscription_tokens")