Replace Jest with node:test and remove matcher dependency

[Copilot]

This updates the test stack from Jest to Node’s built-in node:test runner and removes the temporary external matcher dependency. The test suite now runs on the standard Node toolchain with built-in assertions only.

• Runner migration

  • Replace Jest-based test and testWatch scripts with node --import tsx --test
  • Remove the obsolete Jest configuration and Jest-specific dev dependencies

• Assertion cleanup

  • Replace expect(...) matchers with node:assert/strict
  • Use deepStrictEqual, notStrictEqual, and partialDeepStrictEqual where the existing tests relied on equality, defined-ness, or partial object matching

• Dependency reduction

  • Drop the added expect package so the test stack depends only on node:test + tsx

• Docs alignment

  • Update contributor-facing instructions to describe the new test commands and single-file test invocation

import { describe, test } from 'node:test';
import assert from 'node:assert/strict';

test('finds JSX element names', () => {
  const nodes = query(code, '//JSXOpeningElement/:name/:name');
  assert.deepStrictEqual(nodes, ['div', 'span']);
});