Add lint rule to prevent ObservableScope resource leaks

The rule of thumb to avoid resource leaks is that you should never call ObservableScope methods in a callback unless the ObservableScope is directly passed to or created inside that callback. I had a go at codifying this as a lint rule.

knip.ts

@@ -11,7 +11,7 @@ export default {
   vite: {
     config: ["vite.config.ts", "vite-embedded.config.ts", "vite-sdk.config.ts"],
   },
-  entry: ["src/main.tsx", "i18next.config.ts"],
+  entry: ["src/main.tsx", "eslint/index.js", "i18next.config.ts"],
   ignoreBinaries: [
     // This is deprecated, so Knip doesn't actually recognize it as a globally
     // installed binary. TODO We should switch to Compose v2: