docs: refresh client producer benchmarks

[NikolayS]

Summary

Refresh the client producer benchmark data before 0.2.0 GA:

• reran Python / Go / TypeScript producer benchmarks on GitHub Actions PostgreSQL 18
• added the raw benchmark CSV used by the chart
• added a small SVG render script so the chart is reproducible instead of hand-edited
• refreshed the SVG and docs with the new set-based send_batch numbers

Benchmark run: https://github.com/NikolayS/PgQue/actions/runs/26383024550
Issue: #242

Gates

• GitHub Actions benchmark workflow run 26383024550 passed
• python3 benchmark/charts/render_client_producer_batch_api.py
• SVG XML parse OK
• CSV row/count and speedup sanity check OK