fix(playwright): make qase.step expectedResult and data optional

[gibiw]

Summary

Fixes #981.

qase.step in playwright-qase-reporter typed expectedResult and data as string | undefined but positionally required them. This meant the documented callback-free calls did not compile:

qase.step('action')                  // ts(2554): Expected 3 arguments, but got 1
qase.step('action', 'expected')      // ts(2554): Expected 3 arguments, but got 2

Callers were forced to pass undefined explicitly to omit optional arguments.

Changes

• Mark expectedResult and data as optional (?) in the qase.step signature. Body logic is unchanged — fully backward compatible (existing 3-argument calls and calls passing undefined still work identically).
• Clarify the docstring: qase.step is a title decorator meant to be passed to Playwright's test.step(), not a step runner. Added a one-argument example.
• Add tests for the one- and two-argument forms that previously failed to type-check.

Scope

This PR covers only the type fix (requests #1 partially and #2 from the issue). The ergonomic callback overload (qase.step(title, callback), request #3) and the external docs update on developers.qase.io are out of scope for this change.

Verification

• npm run build — 0 errors; generated dist/playwright.d.ts now shows step(action: string, expectedResult?: string, data?: string): string
• npm test — 101 passed (2 new)
• npm run lint — 0 errors