fix: Prevent $state bigints incrementing and decrementing from throwing

[Ocean-OS]

Closes #14484. Now, incrementing or decrementing BigInt $states will not throw an error. A test has been added for this.

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[Rich-Harris]

preview: https://svelte-dev-git-preview-svelte-14485-svelte.vercel.app/

this is an automated message

[github-actions]

Playground

pnpm add https://pkg.pr.new/svelte@14485

[dummdidumm]

Thanks! can you add a changeset?

[Rich-Harris]

thanks!