Add CrossEncoder to the Sentence Transformers "How to Use" snippet & patch SetFit (#1337)

Hello!

## Pull Request overview
* Add CrossEncoder to the Sentence Transformers "How to Use" snippet
* Patch "How to Use" for SetFit models (that are also tagged as Sentence
Transformers)

## Details
This PR adds the `CrossEncoder` class to the "How to Use" snippets. I'm
working on feature parity of these models with the more common
`SentenceTransformer` models, and the recent Sentence Transformers v4.0
release was a big step in that.
We're already at 150 models:
https://huggingface.co/models?pipeline_tag=text-ranking&library=sentence-transformers

Beyond that, this ensures that `[widgetExample.source_sentence,
...widgetExample.sentences]` doesn't crash, apparently that currently
happens for some SetFit models, e.g.:
https://huggingface.co/faodl/setfit-paraphrase-mpnet-base-v2-5ClassesDesc-multilabel-augmented?library=sentence-transformers

- Tom Aarsen

Author: tomaarsen

packages/tasks/src/model-libraries-snippets.ts

@@ -920,13 +920,32 @@ export const sampleFactory = (model: ModelData): string[] => [
 
 function get_widget_examples_from_st_model(model: ModelData): string[] | undefined {
 	const widgetExample = model.widgetData?.[0] as WidgetExampleSentenceSimilarityInput | undefined;
-	if (widgetExample) {
+	if (widgetExample?.source_sentence && widgetExample?.sentences?.length) {
 		return [widgetExample.source_sentence, ...widgetExample.sentences];
 	}
 }
 
 export const sentenceTransformers = (model: ModelData): string[] => {
 	const remote_code_snippet = model.tags.includes(TAG_CUSTOM_CODE) ? ", trust_remote_code=True" : "";
+	if (model.tags.includes("cross-encoder") || model.pipeline_tag == "text-ranking") {
+		return [
+			`from sentence_transformers import CrossEncoder
+
+model = CrossEncoder("${model.id}"${remote_code_snippet})
+
+query = "Which planet is known as the Red Planet?"
+passages = [
+	"Venus is often called Earth's twin because of its similar size and proximity.",
+	"Mars, known for its reddish appearance, is often referred to as the Red Planet.",
+	"Jupiter, the largest planet in our solar system, has a prominent red spot.",
+	"Saturn, famous for its rings, is sometimes mistaken for the Red Planet."
+]
+
+scores = model.predict([(query, passage) for passage in passages])
+print(scores)`,
+		];
+	}
+
 	const exampleSentences = get_widget_examples_from_st_model(model) ?? [
 		"The weather is lovely today.",
 		"It's so sunny outside!",