feat(useAsyncState): add support directly await

[Hfutsora]

Add initialized in the useAsyncState.

Description

Sometimes, using only isReady or isLoading is not very convenient.

For example, in scenarios where multiple events rely on state being triggered, and the execute may not have been completed yet.

We need to use await initialized to ensure that subsequent operations are executed only after the state has been initialized.

Example

<script lang="ts" setup>
const { initialized, state } = useAsyncState(p1, 0, { immediate: true })

const eventA = async () => {
  await initialized.value
  // do something with the state...
}
const eventB = async () => {
  await initialized.value
  // do something with the state ...
}
</script>

[antfu]

I think instead, we could return a then method to proactively wait for current promises. You could refer to useFetch

[Hfutsora]

Thank you for your suggestion. I have modified the original design to return a thenable object.