render and styleToString exports need file types

[Jody Doolittle]

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:

svelte-email/src/lib/index.ts

Line 15 in c7456ba

 import { render } from './render'; 

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