Cut e2e wall time back toward 10 minutes

The E2E Tests workflow on main took 13 min 40 s at 5b80a64 and at 7939147, up from about 10 min at aa95c0a and c8f64a7. These are run creation-to-update times from gh run list --workflow "E2E Tests" --branch main, read on 2026-11-09. Every PR that touches Go waits for this job before it can be called ready, so in the v0.2.0 batch it sat on the critical path of every code PR.

Most of the growth is the quiet-node specs that Q50 added. Q50's author measured all seven at 190.5 s in one run and about 209 s in a later one. Two of them mostly wait on real timers: retries-backoff takes about 65 s, against the controller's 60 s backoff, and stays-quiet takes about 59 s. The suite grew from 25 specs (about 393 s of go test on c8f64a7, run 42306353731) to 32 specs.

make test-e2e now runs go test with -timeout 20m (Makefile:175), after a run on 333e873 hit the old 10m default. At 13 min 40 s, that leaves about 6 min of margin before the suite fails on time alone.

Things to measure before choosing:

• Make the 60 s backoff and the quiet window configurable in the e2e deployment, so the timer specs wait seconds instead of a minute.
• Run independent specs in parallel (ginkgo -p), if the shared kind cluster allows it.