fix: ensure reactions of non-updating deriveds have their version synced

[trueadm]

This fixes #15414. However, we have a test that fails with this change derived-write-read-write-read. That's because the new logic prevents over-firing the effect in this case, as per design.

So we have two options:

• we state that deriveds are pure and thus can over-fire in some cases – this is already true for unowned deriveds. There's nothing technically wrong with this behaviour.
• we remove the existing failing test and go with this strategy

[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-svelte-15434-svelte.vercel.app/

[github-actions]

Playground

pnpm add https://pkg.pr.new/svelte@15434

[changeset-bot]

🦋 Changeset detected

Latest commit: 3028e7a

The changes in this PR will be included in the next version bump.

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[paoloricciuti]

I would say if we have to chose I lean towards keeping the test and just state that deriveds can overfire

[trueadm]

Agreed