Consider making UseFocus::attribute an opaque type.

[Tropix126]

Currently the user can pass their own accesskit ID into a11y_id, which is intended for UseFocus at the moment due to having all types public:

use dioxus_core::AttributeValue;
use freya_node_state::CustomAttributeValues;

#[allow(non_snake_case)]
#[component]
pub fn BadComponent() -> Element {
    rsx!(
        rect {
            a11y_id: AttributeValue::any_value(
                CustomAttributeValues::AccessibilityId(accesskit::NodeId(0))
            ),
        }
    )
}

This is bad, because it allows the user to pass a duplicate accessibility ID which can mess up the tree in unexpected ways. Generally accesskit node IDs shouldn't be exposed to users at all, since they can't know the current value of the ID counter (thus allowing for overlap with any given u64). To fix this, we can make UseFocus::attribute return an opaque wrapper type over accesskit::NodeId with the NodeId itself not publicly exposed, making the only way to generate it being through a use_focus hook.

pub struct FocusAttribute(AccessibilityId); // AccessibilityId is not publicly exposed, so this struct can't be user-created

// ...

impl UseFocus {
    // ...

    /// Create a node focus ID attribute
    pub fn attribute(&self) -> AttributeValue {
        AttributeValue::any_value(CustomAttributeValues::Focus(
            FocusAttribute(self.id)
        ))
    }
}

This will enforce the invariant that accessibility IDs must first go through the AccessibilityGenerator counter.

pub fn Component() -> Element {
    let focus = use_focus();

    rsx!(
        rect {
            a11y_focus: focus.attribute(),
            // ...
        }
    )
}