ReadStore::from requires that the underlying Lens is Writeable

[MonaMayrhofer]

Problem

When you have a ReadStore and use a lensing function to access one of its fields, that resulting store cannot be converted into another ReadStore.

Aka. you cannot map a ReadStore to a ReadStore

Steps To Reproduce

        #[derive(Store, Default)]
        struct Thing {
            entry: String,
        }
        let a = Store::new(Thing::default());
        let b = ReadStore::from(a);

        let b_entry = b.entry();
        let b_entry_read = ReadStore::from(b.entry());

22:41:52 [cargo] error[E0277]: the trait bound `dioxus::prelude::ReadSignal<Thing>: Writable` is not satisfied
   --> crates/story-teller-app/src/components/townsquare/seat_circle.rs:558:28
    |
558 |         let b_entry_read = ReadStore::from(b.entry());
    |                            ^^^^^^^^^ the trait `Writable` is not implemented for `dioxus::prelude::ReadSignal<Thing>`

Expected behavior

It seems to me that this should be possibe, as it feels like a common use case to receive a ReadStore in a component, and then pass a lensed ReadStore into a deeper component.

Environment:

• Dioxus version: v0.7.1
• Rust version: 0.97.0-nightly
• App platform: web

Questionnaire

I'm interested in fixing this myself but don't know where to start.

[ealmloff]

I think this bound is wrong

dioxus/packages/stores/src/store.rs

Lines 204 to 219 in c64415c

	impl<__F, __FMut, T: ?Sized, S, Lens> ::std::convert::From<MappedStore<T, Lens, __F, __FMut>>
	for ReadStore<T, S>
	where
	Lens: Writable<Storage = S> + 'static,
	__F: Fn(&Lens::Target) -> &T + 'static,
	__FMut: Fn(&mut Lens::Target) -> &mut T + 'static,
	S: BoxedSignalStorage<T> + CreateBoxedSignalStorage<MappedMutSignal<T, Lens, __F, __FMut>>,
	T: 'static,
	{
	fn from(value: MappedStore<T, Lens, __F, __FMut>) -> Self {
	Store {
	selector: value.selector.map_writer(::std::convert::Into::into),
	_phantom: ::std::marker::PhantomData,
	}
	}
	}

[MonaMayrhofer]

I have created a PR: #5607