fix: set correct parent for lazily created derived inside SvelteDate

[JaiWey]

Fixes #18419

The deriveds inside SvelteDate are created lazily, previously the parent effect property could possibly be a to-destory branch effect, which makes the derived shared between multiple components inert after the branch is destroyed. So similar to the #reaction, add an #effect property to save, set and restore the correct effect inside SvelteDate.

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Tests and linting

• Run the tests with pnpm test and lint the project with pnpm lint

[pkg-svelte-dev]

Install the latest version of svelte from 94a71ef:

pnpm add https://pkg.svelte.dev/svelte/c/94a71ef6535cd0592fc9ce20716944e7dfa6d0ff

Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/svelte/pr/18509

Note

This PR is from a fork. A maintainer must approve approve each commit before it can be built and installed.

[changeset-bot]

🦋 Changeset detected

Latest commit: 94a71ef

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

This PR includes changesets to release 1 package

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svelte	Patch

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