Not accepting str as value for interval/date columns

[riwu]

• asyncpg version: 0.29.0
• PostgreSQL version: 15.7
• Do you use a PostgreSQL SaaS? If so, which? Can you reproduce
  the issue with a local PostgreSQL install?: local
• Python version: 3.11
• Platform: Windows
• Do you use pgbouncer?: No
• Did you install asyncpg with pip?: Yes
• If you built asyncpg locally, which version of Cython did you use?: N/A
• Can the issue be reproduced under both asyncio and
  uvloop?: yes

I am using asyncpg as the driver for SQLAlchemy.

class Table(Base):
    __tablename__ = 'table'
    interval: Mapped[timedelta]

session.add(Table(interval='1 min'))

With the above code, it throws this error:
sqlalchemy.exc.DBAPIError: (sqlalchemy.dialects.postgresql.asyncpg.Error) <class 'asyncpg.exceptions.DataError'>: invalid input for query argument $9: '1 min' ('str' object has no attribute 'days')

However, Postgresql accepts '1 min' as a value to an interval column. Why is asyncpg forbidding str even though Postgresql accepts it in this case?