fix: derived reactivity and perf regressions

[hmnd]

fixes sveltejs/kit#15059, fixes #17342, fixes #17111, fixes #17323

#17105 resulted in a few regressions to how deriveds with no dependencies are treated. At worst, it broke reactivity for deriveds in branch effects, but I realized it also casued perf regressions like #17342. Both are now addressed, with test to match.

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[changeset-bot]

🦋 Changeset detected

Latest commit: d117320

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

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[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-svelte-17362-svelte.vercel.app/

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Playground

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