add unit test coverage for QaRankingCodegen

[aglinxinyuan]

Task Summary

Add a dedicated QaRankingCodegenSpec.scala that pins the payload/parse Python-snippet contract of QaRankingCodegen — the Hugging Face codegen for the question-answering / ranking task family. Mirror the existing TextGenCodegenSpec (same package) as the template.

Background

QaRankingCodegen (common/workflow-operator/src/main/scala/org/apache/texera/amber/operator/huggingFace/codegen/QaRankingCodegen.scala) is an object extends TaskCodegen. It produces two Python source snippets — payloadPython(ctx) and parsePython(ctx) — that are spliced into the generated inference operator. It handles five HF pipeline tasks and, like every codegen, must reference self.* attributes rather than inlining raw user strings from the CodegenContext.

override val task: String = "question-answering"
override val tasks: Set[String] = Set(
  "question-answering", "table-question-answering",
  "zero-shot-classification", "sentence-similarity", "text-ranking"
)

Behavior to pin

Member	Contract
task	equals "question-answering"
tasks	equals exactly the 5-element set above
payloadPython	opens with if task == "question-answering":; has an elif branch for table-QA, zero-shot, sentence-similarity and text-ranking; ends with the else: payload = {"inputs": prompt_value} fallback
parsePython	the QA / table-QA branches read body.get("answer", ...); zero-shot / sentence-similarity / text-ranking return json.dumps(body)
no raw-value leakage	with sentinel CodegenContext string fields (e.g. contextColumn / candidateLabels / sentencesColumn set to distinctive "MARKER_…" values), neither snippet contains the sentinel — the code references self.CONTEXT_COLUMN / self.CANDIDATE_LABELS / self.SENTENCES_COLUMN instead

Build the CodegenContext with a small makeCtx helper exactly like TextGenCodegenSpec (set task = "question-answering" plus the QA-specific columns). Assert on snippet structure / marker substrings, not on exact whitespace.

Scope

• New spec: QaRankingCodegenSpec.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