[feat]: allowing all fields to be set as default for FromPyObject

[WSH032]

In #4829 (comment), FromPyObject was intentionally designed to disallow all fields being set with #[pyo3(default)]. I wonder if this is because:

ref: #4829 (comment)

the surprising behavior that a variant Foo { #[pyo3(default)] value: usize } becomes a catch-all just like the Foo {} variant.

However, for me, this behavior makes sense, as I use it to extract class Foo(TypedDict, total=False) for typed kwargs.

// 💥 cannot derive FromPyObject for structs and variants with only default values
#[derive(FromPyObject)]
#[pyo3(from_item_all)]
pub struct Foo {
    #[pyo3(default)]
    id: Option<i32>,
}

#[pyfunction]
#[pyo3(signature = (**kwargs))]
fn foo(kwargs: Option<&Bound<'_, PyDict>>) -> PyResult<()> {
    let foo: Option<Foo> = kwargs.map(|kwargs| kwargs.extract::<Foo>()).transpose()?;
    Ok(())
}

from typing_extensions import NotRequired, TypedDict, Unpack


class Foo(TypedDict, total=False):
    id: NotRequired[int]


def foo(**kwargs: Unpack[Foo]) -> None: ...

foo()  # ok
foo(id=1)  # ok
foo(id=1, foo=2)  # Err: no `foo` parameter