fix: skip static optimisation for stateless deriveds after await

[Rich-Harris]

For expressions that we know will not change, we set text content during component initialisation rather than in an effect:

p.textContent = 'whatever';

This fails if the right-hand side isn't known at initialisation time, and in the case of a derived that comes after an await but has no dynamic dependencies...

<script>
	await 0;
	let message = $derived('hello');
</script>

<p>{message}</p>

...it results in $.get(undefined), since the derived isn't created until after initialisation. This fixes it.

It's a real edge case, but it's one I ran into while looking into #17271 — will self-merge once green to unblock further exploration.

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