test(context): cover NodeList for include/exclude and fix doc examples

[cycsmail]

The context.md examples labeled "Test a Node list" and "Test everything except these DOM nodes" used document.querySelector(...), which only ever returns a single node, so they didn't actually show a NodeList. Switched both to document.querySelectorAll(...) and tweaked the comments so the examples demonstrate the NodeList support that already works. Also added two Context unit tests: one for a NodeList passed as the bare context, and one for NodeLists passed via include/exclude. (doc/API.md already lists NodeList as an accepted context, so it didn't need a change.)

Heads up: I couldn't get the browser test runner going in my environment, so the new assertions were checked against the built axe.js bundle under jsdom rather than web-test-runner — prettier and eslint are clean. Worth a CI run to confirm in-browser.

Closes: #3348

[CLAassistant]

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[straker]

I couldn't get the browser test runner going in my environment, so the new assertions were checked against the built axe.js bundle under jsdom rather than web-test-runner — prettier and eslint are clean

Interesting. What environment are you running where that didn't work? We just switched over to web test runner so I'd like to make sure it's usable for anyone who wants to work in axe-core.

[cycsmail]

Chrome-for-Testing downloaded fine but the browser wouldn't launch in my container — needed --no-sandbox and was missing the usual system libs (libnss3, libgbm, libasound2…). So I ran the same assertions through the jsdom path against the built axe.js instead. The two tests are in the normal browser suite though, so they'll run fine in your CI.

If you want it smoother for container/CI folks, passing --no-sandbox --disable-dev-shm-usage in the launcher + a note on the apt deps would cover most headless setups.

[cycsmail]

Update — sorted the browser in my container (system libs + --no-sandbox) and ran the full web-test-runner suite this time. Both new NodeList tests pass in real Chromium, whole suite green (8,304 across 124 files) — holds up in-browser, not just the jsdom check.