cut CI runtime

CI takes about an hour. Critical path is lint -> tests (18m55s) -> integration (45m10s windows).

Measured on #7800:

job	ubuntu	macOS	windows
Integration	9m52s	11m38s	45m10s
Tests	18m55s	14m51s	17m45s
Functional	9m58s	8m56s	16m41s
Release test	23m53s

ubuntu integration is already under 10m, so this is a windows problem, not a suite problem. The suite spawns ~175 nuclei processes against a ~200MB binary.

Ruled out by measurement:

• fuzz ~8.1s/case and headless ~6.8s/case; those 28 cases outweigh the other 147. javascript is ~0.15s/case.
• Harness setup is ~19s per go test run, paid once.
• Raising PARALLELISM is worse: fuzz 137s at 4, 294s at 12. Each spawned nuclei is itself concurrent.
• -no-interactsh on cases that do not need it: no measurable saving.
• Running in process instead of spawning: ~8% on macOS, and breaks cases that then share process state.