Add row_factory to Python bindings

[russellromney]

A very useful thing in python sqlite3 is the row factory. I'd like to add a standard Dict row factory and a dataclass row factory, and also document how to add your own (so we don't bundle pydantic).

Example implementaiton:

def dict_row(cursor, row):
    return dict(zip([d[0] for d in cursor.description], row))

def dataclass_row(cls):
    def factory(cursor, row):
        return cls(*row)  # or use field names if needed
    return factory

In docstring:

# User can do this themselves:
def pydantic_row(model):
    def factory(cursor, row):
        cols = [d[0] for d in cursor.description]
        return model(**dict(zip(cols, row)))
    return factory

In use:

from turso import Row, dict_row, dataclass_row

conn.row_factory = dict_row  # {"col": val}
conn.row_factory = dataclass_row(User)  # User(id=1, name="alice")

I will likely pull a PR for this if it seems like a good idea - I like it to echo python's sqlite3 semantics.