head extension mishandles title

The trouble with the title tag appears when using the extension with `hx-head="append"`.
The title is something that intrinsically changes between pages and so when using `append` it will cause multiple titles to appear.
The problem affects the extension for both htmx v2 and v4.

For my local workaround, I disable title handing entirely, since htmx already handles titles itself and so there's an argument that it's not the extension's responsibility to manage them at all.

Here is a simple reproduction with two pages using boosting. Toggling between the two results in multiple title elements.
**Page 1**
```html

Page 1


Page 2

```
**Page 2**
```html

Page 2


Page 1

```

Start with the hx-head extension entry point and reproduce the behavior using the two HTML pages in the issue with hx-head="append" and boosted navigation. Trace how title elements are handled between Page 1 and Page 2; done means toggling between them no longer leaves multiple title elements, for both htmx v2 and v4.

Written by the indexing model from the issue text.