Benchmark: label throughput as tests/s and flip the throughput chart

- Rename the throughput unit from "ops/s" to "tests/s" in the Totals table
  column, the throughput section heading, and the chart title/dataset label/alt
  text (per-operation latency stays in ms). The value is unchanged — it is still
  the JMeter Total throughput (total samples/sec), just relabeled.
- Flip the Total throughput chart to a horizontal bar chart (type:horizontalBar),
  so the two servers sit on the vertical axis and throughput runs along the
  horizontal axis; widen it to suit horizontal bars.