add unit test coverage for ImageTaskCodegen

[aglinxinyuan]

Task Summary

Add a dedicated ImageTaskCodegenSpec.scala that pins the payload/parse Python-snippet contract of ImageTaskCodegen — the Hugging Face codegen for the image-pipeline task family (9 tasks). Mirror the existing TextGenCodegenSpec (same package) as the template.

Background

ImageTaskCodegen (common/workflow-operator/src/main/scala/org/apache/texera/amber/operator/huggingFace/codegen/ImageTaskCodegen.scala) is an object extends TaskCodegen and the richest codegen of the family. It splits into image-only tasks (raw image bytes as the request body) and image + prompt tasks (base64 image bundled with a text prompt in a JSON payload), plus a validation path.

override val task: String = "image-classification"
override val tasks: Set[String] = Set(
  "image-classification", "object-detection", "image-segmentation", "image-to-text",
  "visual-question-answering", "document-question-answering",
  "zero-shot-image-classification", "image-text-to-text", "image-to-image"
)

Behavior to pin

Member	Contract
task	equals "image-classification"
tasks	equals exactly the 9-element set above
payloadPython (image-only)	tasks in image_only_tasks set payload = current_image_bytes, use_raw_binary_body = True, raw_binary_headers = image_headers
payloadPython (VQA / doc-QA)	build a payload with self._image_input_as_base64(current_image_bytes) and "question": prompt_value
payloadPython (zero-shot)	raise ValueError(...) when fewer than 2 candidate labels are supplied
parsePython	image-to-text / image-text-to-text read choices[0].message.content; URL responses are normalized via self._url_to_data_url; classification/detection/segmentation return json.dumps(body)
no raw-value leakage	with sentinel CodegenContext fields (e.g. imageInput / inputImageColumn / candidateLabels = "MARKER_…"), neither snippet contains the sentinel

Build the CodegenContext with a makeCtx helper as in TextGenCodegenSpec. Assert on snippet structure / marker substrings, not exact whitespace.

Scope

• New spec: ImageTaskCodegenSpec.scala under common/workflow-operator/src/test/scala/org/apache/texera/amber/operator/huggingFace/codegen/.
• No production-code changes.

Task Type

• Refactor / Cleanup
• DevOps / Deployment / CI
• Testing / QA
• Documentation
• Performance
• Other

[PG1204]

/take