[pull] main from GoogleCloudPlatform:main

[pull]

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Created by pull[bot] (v2.0.0-alpha.4)

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Summary by cubic

Updates all RAG Python samples to the latest agentplatform RAG module and google.genai for generation, replacing legacy vertexai usage. Aligns examples and tests with new types, client init, and response formats.

• Refactors

  • Replaced vertexai.rag with agentplatform.Client.rag and agentplatform.types; updated return types and hints across samples.
  • Switched generation to google.genai (models.generate_content) with Tool/Retrieval from google.genai.types; uses MODEL_ID (e.g., gemini-3.5-flash) or gemini-2.5-pro in examples.
  • Migrated corpus and vector DB configs (Vertex Vector Search, Pinecone, Weaviate, Feature Store) to new RagVectorDbConfig shapes.
  • Reworked file import to ImportRagFilesConfig with GcsSource and optional GoogleDriveSource, plus chunking via RagFileTransformationConfig; added async variant via client.aio.rag.
  • Updated list APIs to response wrappers (ListRagCorporaResponse, ListRagFilesResponse); tests now read .rag_corpora and .rag_files.

• Migration

  • Use agentplatform and google-genai; remove vertexai RAG API calls.
  • Initialize once with agentplatform.Client(project, location) and call via client.rag (or client.aio.rag for async).
  • Set MODEL_ID env var for generation samples; when importing from GCS, use wildcard paths like gs://bucket/dir/*.

^{Written for commit 8b6869e. Summary will update on new commits.}