Convert `HttpOptions` files to `UploadedFile`'s

Currently, uploading files is a bit verbose:

```php
$browser->post('/endpoint', ['files' => [new UploadedFile($realpath, $name, test: true)]);
```

It would be better if you could do:

```php
$browser->post('/endpoint', ['files' => [$realpath]);
```

And `HttpOptions` auto-converts file paths's to `UploadedFile`'s.