perf(pd): omit unused output logprob metadata

[WANDY666]

Summary

• Mark OpenAI chat requests, and completions requests without logprobs, as not needing output-token logprob metadata on the PD wire.
• Preserve that transport-only marker across PD master's ctypes sampling-parameter copies, split blocks, multiple choices, and batched completion prompts.
• Drop id, logprob, cumlogprob, special, and logprobs only when the caller does not consume them.
• Keep legacy behavior by default for other APIs and sampling params without the marker.

Why

The common OpenAI path was forwarding per-token metadata that its response builders never read. This PR isolates metadata elision from the tuple wire-format change so its API contract and fallback behavior can be reviewed independently.

Validation

• Production-code diff passes repository black and flake8 hooks.