Optimize Outbound Messages In A Batch

Queue many outbound drafts for the optimizer in one request and get a batch_id back at once. Use when a campaign has more drafts than the per-workspace limits on single optimizes allow, or nobody is waiting on each result. Items run later on spare capacity, behind interactive calls, and are never refused as busy. Poll the batch for counts, an estimated finish time and each result. Only items that succeed count as usage.