attrs.field(converter=None) makes field type Unknown instead of keeping the annotation #5283

When an attrs field is annotated (e.g. x: int) and converter=None is passed explicitly, Pyrefly treats the field / synthesized __init__ parameter as Unknown instead of int.

Expected behavior:
converter=None means “no converter” (same as omitting converter, default argument), so the init parameter should still be typed from the field annotation (int).

Minimal Repro

from attrs import define, field

@define
class A:
    x: int = field(converter=None)
p = A("asd")  # should be a type error; currently accepted (field typed as Unknown)

Environment
Pyrefly 1.4
attrs 25.3.0