Discussed in #8023

I think we should try to hit this in terms of all the async dialects all of which have to do what we are doing here, which would be that we make a common mixin / base for all the async-adapted DBAPIs. for asyncpg it would be used here:

    from ..exc import EmulatedDBAPIException

    class Error(EmulatedDBAPIException):
        pass

that way people can look at EmulatedDBAPIException to see the fields, which would be like:

class EmulatedDBAPIException:
    """an exception class used to adapt non-DBAPI database driver exceptions
    into DBAPI exceptions"""

    message: str
    """string message indicating the error"""

    orig: Exception
    """the original driver-level exception object"""

that looks kind of boring so we can also add an accessor on

that way someone that knows asyncpg can receive the top level SQLAlchemy DBAPIException and just refer to .driver_exception to get all the asyncpg fields.