fix: implement upsert_vector for MarqoVectorStoreDriver

[biconcavelens]

• I have read and agree to the contributing guidelines.

Describe your changes

MarqoVectorStoreDriver.upsert_vector previously raised NotImplementedError. Marqo supports upserting arbitrary vectors through custom vector fields, so this implements it:

• Builds a document with a custom_vector mapping and upserts it via add_documents, mirroring the existing upsert method in the same driver (namespace/meta handling, response parsing, and returning the _id).
• Removes the now-inaccurate Raises: ... not yet implemented line from the docstring.
• Adds unit tests covering the basic upsert and the namespace/meta passthrough, using the existing mocked Marqo client fixture.

Note: unlike the PineconeVectorStoreDriver, **kwargs is intentionally not forwarded to add_documents, since Marqo's add_documents has a fixed signature (no **kwargs) — this matches the existing upsert method in this driver.

Issue ticket number and link

Closes #1802 — #1802

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AI assistance disclosure (per CONTRIBUTING.md): this change was drafted with AI assistance. The implementation follows the pattern of the existing upsert method and the issue author's suggested approach; I verified custom_vector is a valid Marqo mapping type and that add_documents does not accept arbitrary kwargs against the pinned marqo version, and confirmed the full driver test suite passes locally (pytest) with ruff check/format clean.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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