What is the @AutoClose extension and how does it simplify resource management in JUnit 6?

import org.junit.jupiter.api.AutoClose;

class AutoCloseDemo {

    // Closed after each test method (instance-scoped)
    @AutoClose
    private final Connection db = DriverManager.getConnection(TEST_DB_URL);

    // Closed once after all tests (static = class-scoped)
    @AutoClose
    private static final HttpClient httpClient = HttpClient.newHttpClient();

    @Test
    void queryUsers() throws SQLException {
        // db is open and ready; closed automatically after this test
        try (PreparedStatement ps = db.prepareStatement("SELECT * FROM users")) {
            ResultSet rs = ps.executeQuery();
            assertTrue(rs.next());
        }
    }

    @Test
    void callExternalApi() throws Exception {
        // httpClient is open; closed once after all tests complete
        HttpResponse<String> resp = httpClient.send(
            HttpRequest.newBuilder(URI.create("https://api.test.com")).build(),
            HttpResponse.BodyHandlers.ofString()
        );
        assertEquals(200, resp.statusCode());
    }
}
// No @AfterEach or @AfterAll needed for these resources!

// Equivalent JUnit 5 code (before @AutoClose):
class JUnit5Equivalent {
    private Connection db;
    @BeforeEach void setUp() throws SQLException {
        db = DriverManager.getConnection(TEST_DB_URL);
    }
    @AfterEach void tearDown() throws SQLException {
        if (db != null) db.close();  // <-- boilerplate eliminated by @AutoClose
    }
}