Go Speedtest HTTP engines

@cloudflare/speedtest 1.15.0 - Copyright Cloudflare, MIT License.
cloudflare.mjs is an unmodified distribution; LICENSE.cloudflare.txt is included.
The application uses an isolated fetch adapter to measure completed payloads and
full elapsed time; Cloudflare's aggregated bandwidth summary is not reported.
External telemetry, AIM logging, RPKI and TURN checks are disabled.

LibreSpeed speedtest_worker.js - Federico Dossena and contributors, GNU LGPLv3.
Unmodified worker source is served at librespeed-worker.js alongside its license.
Source: https://github.com/librespeed/speedtest
Settings: overheadCompensationFactor=1, explicit streams and measurement duration.

Object sampling and UI adapters in http-engine.js and object-worker.js are part
of this Go Speedtest application. HTTP object results and sustained throughput
results are separate measurement modes and must not be compared as one metric.