render and styleToString exports need file types

[doolijb]

Playwright test fails to import svelte-email.

Error: Cannot find module '/srv/www/app/node_modules/svelte-email/render' imported from /srv/www/app/node_modules/svelte-email/index.js

Solution: https://github.com/carstenlebek/svelte-email/blob/c7456ba19b464c253f0f8a13d039e11f5f4d04b8/src/lib/index.ts#L15

import { render } from './render'; // update to './render.d.ts'
import { styleToString } from './utils'; // update to './utils.d.ts'