Add type definition for SvelteToastOptions

[domuk-k]

The src/lib/index.js file currently lacks a type definition for SvelteToastOptions.

import { toast } from '@zerodevx/svelte-toast';
// ❌ import type { SvelteToastOptions } from '@zerodevx/svelte-toast/stores'; 
/** "/stores"  is not exposed  */ 

// 😔 export type SvelteToastOptions = Parameters<typeof toast.push>[1];

function customToast(message: string, options: SvelteToastOptions) {
   toast(message, options);
}

This change will offer a better development experience for developers using the SvelteToast library.

[zerodevx]

Hey, thanks so much for the PR - moving the conversation to #107