Use Processors as Notebook Filters?

Following up on #1228

We used to rely on [notebook filters](https://quarto.org/docs/extensions/nbfilter.html) for processing notebooks, which had the upside that you could use nbdev directives in your Quarto project in a really lightweight way. We stopped using notebook filters for performance reasons. However, I wonder if it is possible to provide an interface to nbdev Processors that can modify notebooks through the stdin/stdout interface so people can still use these directives in their Quarto blogs in a lightweight fashion, especially if they decide to develop extensions.

The goal is that the only thing that people have to do enable nbdev directives in their plain quarto projects is make a one-line change in their `_quarto.yml` file like this:

```
---
ipynb-filters: nbdev_filters
---
```

@jph00 @seeM WDYT

cc: @muellerzr

Leggi la discussione in #1228 e le interfacce esistenti nbdev Processor e notebook-filter descritte nell’issue. Analizza come un Processor potrebbe usare stdin/stdout con l’entry point ipynb-filters di Quarto. Il lavoro è completato quando semplici progetti Quarto possono abilitare le direttive nbdev con l’impostazione di una sola riga mostrata in `_quarto.yml`.

Scritto dal modello di indicizzazione a partire dal testo della issue.