(feat) Add Turbopuffer namespace pinning CLI

[jamesgao-jpg]

Summary

• Add --pin-namespace/--no-pin-namespace and --pin-replicas to the Turbopuffer benchmark CLI.
• PATCH Turbopuffer namespace metadata to request pinning before benchmark operations when explicitly enabled.
• Add TurboPufferUnpin CLI command to clear namespace pinning after benchmark runs.

Test Plan

• python -m py_compile vectordb_bench/backend/clients/turbopuffer/cli.py vectordb_bench/backend/clients/turbopuffer/config.py vectordb_bench/backend/clients/turbopuffer/turbopuffer.py vectordb_bench/cli/vectordbbench.py
• Stubbed metadata PATCH smoke test for unpin payload ({"pinning": null}), no real Turbopuffer API calls made.

Notes

• Full test suite was not run in the local checkout because the environment is missing the broader VectorDBBench dependency stack.

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[alexanderguzhva]

@jamesgao-jpg I'm not very familiar with VectorDBBench internals, just in case :) Nevertheless, this TurboPufferUnpin makes me confused, because (as a user) I don't understand why it needed to have it, and there's no description / anything that could explain me this.

[jamesgao-jpg]

@jamesgao-jpg I'm not very familiar with VectorDBBench internals, just in case :) Nevertheless, this TurboPufferUnpin makes me confused, because (as a user) I don't understand why it needed to have it, and there's no description / anything that could explain me this.

I've pondered about where to document this, at the end I can't think of a better location than where the code currently lies, since this is a rather niche thing with turbopuffer (they allow users to pin certain namespace for indefinite duration for more predictable performance).

[alexanderguzhva]

@jamesgao-jpg Please ensure that this is properly documented in readme.md on the https://github.com/zilliztech/VectorDBBench. Also, can this be implemented as a flag to plain Turbopuffer instead of a separate benchmark? I'm not saying whether this is needed to be implemented this way, but I'm asking to confirm the decision.