omit_if_default ignores attrs' converters

Hi! It seems like currently converter with omit_if_default=True does not apply attrs' converters when checking if the value is equal to the default one.

import attrs
import cattrs

c = cattrs.Converter(omit_if_default=True)


@attrs.define
class A:
    b: int = attrs.field(default="0", converter=int)


c.unstructure(A())
# {'b': 0}


@attrs.define
class A:
    b: int = attrs.field(default=0, converter=int)


c.unstructure(A())
# {}

Is this the expected behavior? If so, would you consider changing it?

Start with cattrs.Converter configured with omit_if_default=True and its unstructure path, using the attrs.define examples and attrs.field converters as the reproducer. Determine whether default comparison should use the converted value, then add or update coverage for both default="0", converter=int and default=0; done means the output consistently omits or retains b according to the agreed behavior.