refactor: clean up repo infrastructure and file organization

Types of changes

[x] Chore (a non-breaking change which is related to package maintenance)
[ ] Bug fix (a non-breaking change which fixes an issue)
[ ] New feature (a non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to change)

This PR refactors prismicrichtext-rf by performing the following changes:

Remove unnecessary dependencies
Update all dependencies
Renamed <PrismicRichText>'s richTextSerializer prop to components to match @prismicio/react and @prismicio/vue
Use the latest Svelte package script conventions (see the build script as an example)
Update vite.config.ts to use the latest SvelteKit conventions
Update svelte.config.js to use the latest SvelteKit conventions
Organize the lib directory to match its public API by removing unnecessary nesting
Update dev mode detection using the esm-env package (as recommended by @sveltejs/package)
Merge vite.config.ts and vitest.config.ts

[ ] My change requires an update to the official documentation.
[ ] All TSDoc comments are up-to-date and new ones have been added where necessary.
[ ] All new and existing tests are passing.

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