Set UV_THREADPOOL_SIZE dinamically on startup

[RafaelGSS]

Thread: https://openjs-foundation.slack.com/archives/C049LSE8QBH/p1769010116581549

We came up with a default idea that switching the default 4 threads to:

UV_THREADPOOL_SIZE="$(getconf _NPROCESSORS_ONLN) > 4 ? (getconf _NPROCESSORS_ONLN) : 4"

Might have a good impact on powerful machines. However, before taking any action, we should have some measurements:

1. Benchmark a different set of machines

• 4vCPUs
• 2vCPUs
• 8vCPUs

2. Define a minimal HTTP server that serves a file
3. Provide load on it until 4 threads become saturated (define the threshold)
4. Bump UV_THREADPOOL_SIZE and see how it behaves.

[richardlau]

If you're not aware, libuv also has a uv_available_parallelism heuristic.