feat(prefer-ending-with-an-expect): require tests to end in an assertion

[unlikelyzero]

Adds a prefer-ending-with-an-expect rule, ported from jest/prefer-ending-with-an-expect.

A test that ends with an action rather than an assertion is often unfinished — the setup and interaction got written, but the check that makes the test meaningful never did. It pairs with expect-expect, which only checks that an assertion exists somewhere.

Two Playwright-specific adjustments over the jest version:

• A trailing test.step(...) is accepted as long as that step itself ends with an assertion (recursively), since wrapping the final check in a step is a normal Playwright pattern.
• Options are assertFunctionNames and assertFunctionPatterns, matching this plugin's expect-expect rather than jest's star-pattern assertFunctionNames.

expect.soft(...) and expect.poll(...) count as assertions, and a trailing return expect(...) is unwrapped so it counts too.

Not enabled in the recommended config, matching eslint-plugin-jest.