Every LightcraftApp built by the ui-egui lib tests started the product's
render pool: cores - 1, at most six workers. Several tests run at once
and most build an app, so 4 test threads ran about 24 render workers and
16 ran about 96. Under cfg(test) Renderer::default now starts two
(TEST_WORKERS); a test that needs more asks with with_worker_threads.
The product default is unchanged.
a_test_app_renders_on_two_workers fails without it (6 workers on a
16-core machine).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>