test: rework tests to node-only (#350)

Long ago it seems we stopped testing in a browser, so this removes the
associated switches in the test files and moves to a node-only suite.

Meanwhile, this moves to using c8 for coverage and also reworks the
tests to hit a local server rather than a real one (previously was
hitting `chaijs.com` and another domain or two which changed underneath
it over time).

Author: 43081j

eslint.config.mjs

@@ -11,13 +11,18 @@ export default [
         expect: 'readonly',
         chai: 'readonly',
         global: 'writable',
-        request: 'readonly'
+        request: 'readonly',
+        AbortController: 'readonly',
       }
     }
   },
   {
     ...js.configs.recommended,
     files: ['**/*.js']
   },
-
+  {
+    rules: {
+      'mocha/no-mocha-arrows': 'off'
+    }
+  }
 ];