Probe multiple URLs in parallel with a bounded worker pool; the N samples
of each URL remain sequential to preserve accurate min/avg/max statistics.
Default auto-concurrency is min(numURLs, 8); -c 1 restores serial mode.
Output is always buffered and printed in original input order. Verified
clean with go test -race.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Examples 1-3: clean global sweep (single, 10 samples, JSON).
Examples 4-8: one failure type each (DNS, refused, timeout, HTTP, TLS).
Example 9: full matrix, all 5 failure types in one run.
Example 10: quick smoke test (-n 1, JSON, --timeout 2s, all types).
Includes runtime estimates and jq filter snippets.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
