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/vitest.config.ts

@@ -3,5 +3,9 @@ import { defineConfig } from 'vitest/config';
 export default defineConfig({
   test: {
     environment: 'node',
+    typecheck: {
+      enabled: true,
+      tsconfig: './tsconfig.src.json',
+    },
   },
 });