feat(stdlib): new modules + eslint/tsconfig migration

- Add array/async/etc. modules and type tests; migrate to eslint flat config
  and composite tsconfig (vitest typecheck enabled).
- Fix PubSub.emit to snapshot listeners before iterating (stable EventEmitter
  semantics; avoids invoking listeners added during the same emit).

core/stdlib/tsdown.config.ts

@@ -3,5 +3,6 @@ import { sharedConfig } from '@robonen/tsdown';
 
 export default defineConfig({
   ...sharedConfig,
+  tsconfig: './tsconfig.src.json',
   entry: ['src/index.ts'],
 });