`dioxus-native` writes `disabled: false` as a present attribute

## Environment

- dioxus: `0.8.0-alpha.1` (`.dioxus-main`), `dioxus-native-dom`
- blitz: `0.3.0-beta.2`

## Problem

`rsx! { input { disabled: false } }` renders a control that Blitz treats as
disabled: it gets no default action, so a checkbox/radio never toggles and no
`input` event is dispatched. Every segment of a radio group written this way is
dead.

## Root cause

`set_attribute_impl` (`packages/native-dom/src/mutation_writer.rs`) computes
`is_falsy(value)` and passes it down, but `set_attribute_inner` only acts on it
for one attribute:

```rust
if local_name == "checked" && is_falsy {
docm.clear_attribute(node_id, name);
} else {
docm.set_attribute(node_id, name, value); // Bool(false) -> "false"
}
```

So `AttributeValue::Bool(false)` becomes the *string* `"false"`, and the
attribute is present. Blitz - like HTML - reads boolean attributes by presence
(`blitz-dom/src/events/pointer.rs`, `handle_click`: `let disabled =
el.attr(local_name!("disabled")).is_some();`), so `disabled="false"` disables
the element.

`checked` was presumably special-cased when exactly this bug was hit there.
The same applies to every other HTML boolean attribute: `disabled`, `readonly`,
`required`, `multiple`, `hidden`, `selected`, `open`.

## Reproduction

```rust
rsx! {
label {
input { r#type: "checkbox", disabled: false, oninput: move |_| println!("hit") }
"click me"
}
}
```

Never prints under `dioxus-native`; prints on web. Removing the `disabled`
line, or writing `disabled: false.then_some(true)`, fixes it.

## Workaround in this repo

`libero`'s `Box::attr` already drops falsy attributes, so components built on it
were unaffected. `SegmentedControl` writes its radios in raw `rsx!`, and now
passes `segment.disabled.then_some(true)` so the attribute is absent unless
true.

## Status

Not reported upstream. The fix is to generalise the `checked` special case to
the boolean-attribute set - clear rather than stringify when falsy.

Start in packages/native-dom/src/mutation_writer.rs, reading set_attribute_impl and set_attribute_inner alongside the existing checked handling. Use the provided rsx! reproduction and inspect the boolean-attribute behavior described in blitz-dom/src/events/pointer.rs; done means falsy boolean attributes are absent rather than serialized as "false", while truthy values remain present.

Written by the indexing model from the issue text.