fix: add snippet argument validation in dev

[Ocean-OS]

Fixes #15517 by throwing in dev mode if a snippet is passed invalid arguments— in client, if $$anchor is not a Node or other arguments are not functions, and in server, if $$payload is not a valid payload.

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Tests and linting

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

[changeset-bot]

🦋 Changeset detected

Latest commit: 31b4bb6

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

This PR includes changesets to release 1 package

Name	Type
svelte	Patch

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[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-svelte-15521-svelte.vercel.app/

[github-actions]

Playground

pnpm add https://pkg.pr.new/svelte@15521

[HoldYourWaffle]

Wow, that was fast!
Small mixup: this'd fix #15517, #15518 adds a note about it to the docs :)

[Ocean-OS]

This should be ready for review. I made Payload a class and changed any references to it to reflect this.

[Ocean-OS]

Not sure why tests are failing all of a sudden, they were passing before...