taquba-bulk-v0.1.0

Initial release. Per-batch orchestrator that runs one pipeline over many
inputs in a single process on top of taquba-workflow.

Added

• Pipeline: the per-item contract (typed Input / Output, an Error
  that converts into a StepError, and an async run). Each input item
  becomes one taquba-workflow run whose single step invokes run; the
  pipeline's own logical steps live inside run as BulkCtx::memoized
  calls.
• BulkCtx<T>: per-item execution context. Carries the typed input,
  run_id, and submitter headers; exposes memoized (durable per-step
  result caching so an at-least-once retry replays cached results instead of
  repeating a paid call), record_cost, and cancel_token.
• CostReport: generic named-metric accumulator (token counts, paid-API
  units, compute-seconds, dollars). Interior-mutable while a step runs and
  serializable for the per-item envelope and the batch rollup.
• Bulk / BulkBuilder: the runner. Submits N runs, drives the worker pool,
  streams output as items complete, and aggregates progress and cost.
  Builder options: output, key_fn, headers, max_concurrent,
  poll_interval, queue_name, memo_prefix, fail_threshold. run
  executes to completion; run_with_shutdown drains in-flight items on a
  shutdown signal (e.g. spot preemption).
• ProgressSnapshot: point-in-time counts, rate, estimated time remaining,
  and cost rollup, returned by Bulk::progress.
• BulkReport: final counts, elapsed time, cost rollup, and
  failed_run_ids (re-submitting those ids resumes from cached memo state).
• OutputSink with JsonlSink (one JSON record per line) and NullSink
  (discards records, for side-effecting pipelines); read_jsonl for
  line-delimited JSON input.
• Error / Result: crate error type, including
  Error::FailureThresholdExceeded when the share of failed items crosses
  the configured threshold.
• Re-exports StepError and StepErrorKind from taquba-workflow for the
  Pipeline::Error type.