HTML: improve assertions while chaining

### Description

As a new user of the `\Mantle\Support\HTML` class helper methods, I noticed something that can be prone to induce a user to make a mistake.

I wonder if it is important to help users, either with documentation or maybe with errors so that it doesn't happen or so that the user is aware of them.

### Use Case

For example, take this html:

```html

A user would assume that the `has_class` method is checking the `div` with the id, unaware it is actually checking the whole `string`.
```php
$response->html()
->filter( 'div' )
->eq( 1 )
->assertElementExistsById( 'random-element' )
->has_class( 'unrelated-class-not-in-the-random-element' )
```

So the fact that the HTML class has multiple helpers, including methods from `SymfonyCrawler`, makes it prone to mistakes, particularly while writing unit tests where chaining them is so easy.