feat: add name_manually_edited field to User model and update related functionality

- Introduced a new boolean column `name_manually_edited` in the `users` table to control whether user names are overwritten during synchronization with Telegram.
- Updated the `get_or_create_user` function to respect the `name_manually_edited` flag, ensuring names are only updated when the flag is false.
- Implemented a new function `update_user_display_name` to allow manual updates of user names while setting the `name_manually_edited` flag to true.
- Enhanced unit tests to cover the new functionality and ensure correct behavior of name handling based on the `name_manually_edited` flag.

duty_teller/db/models.py

@@ -1,6 +1,6 @@
 """SQLAlchemy ORM models for users and duties."""
 
-from sqlalchemy import ForeignKey, Integer, BigInteger, Text
+from sqlalchemy import Boolean, ForeignKey, Integer, BigInteger, Text
 from sqlalchemy.orm import DeclarativeBase, Mapped, mapped_column, relationship
 
 
@@ -22,6 +22,9 @@ class User(Base):
     first_name: Mapped[str | None] = mapped_column(Text, nullable=True)
     last_name: Mapped[str | None] = mapped_column(Text, nullable=True)
     phone: Mapped[str | None] = mapped_column(Text, nullable=True)
+    name_manually_edited: Mapped[bool] = mapped_column(
+        Boolean, nullable=False, server_default="0", default=False
+    )
 
     duties: Mapped[list["Duty"]] = relationship("Duty", back_populates="user")