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/src/arrays/last/index.test.ts

@@ -1,4 +1,4 @@
-import { describe, it, expect } from 'vitest';
+import { describe, expect, it } from 'vitest';
 import { last } from '.';
 
 describe('last', () => {
@@ -20,4 +20,10 @@ describe('last', () => {
     expect(last([1, 2, 3], 42)).toBe(3);
     expect(last(['a', 'b', 'c'], 'default')).toBe('c');
   });
+
+  it('preserve a present null/undefined/falsy last element (not the default)', () => {
+    expect(last([1, null as number | null], 42)).toBeNull();
+    expect(last([1, undefined], 42)).toBeUndefined();
+    expect(last([0], 99)).toBe(0);
+  });
 });