refactor(qwen35): split TP response contract into tp_executor/responses.rs

Move the reply envelope (TpWorkerReply/TpWorkerResponse), bounded response
collection, per-command response validation, and the step-timeout/abort
helpers out of tp_executor.rs; the three response-contract tests move with
them. Behavior unchanged, with two behavior-preserving consolidations in
the moved code: validate_exact_rank_responses folds its push loop into an
iterator pipeline, and the three rank-0 payload validators (prefill /
decode / unified) collapse into one validate_primary_responses helper over
payload extractors, keeping the exact prior error messages. Rebased over
pegainfer-project#1004/pegainfer-project#1005/pegainfer-project#1033/pegainfer-project#1038 (the precapture sweep keeps using
validate_ack_responses, which stays production-visible).

Signed-off-by: CAICAIIs <3360776475@qq.com>

Author: CAICAIIs