taquba-bulk-v0.2.0

Changed

• Batch submission runs with bounded concurrency instead of one
  awaited submit at a time. Each submission blocks on a durable
  enqueue commit and concurrent commits share WAL flushes, so serial
  submission capped at one item per flush interval (one item per
  100ms at the SlateDB default). Enqueue order across in-flight
  submissions is not defined; batch items are independent.

Added

• BulkCtx::memoized_by_content and
  BulkCtx::memoized_by_content_with_cached_cost for memoized steps
  whose keys should be derived from serialized input content rather
  than caller-supplied strings.
• BulkCtx::memoized_with_cached_cost for memoized steps whose cost counters
  should be recorded both on fresh compute and on memo hits.