feat(playwright): configurable default timeout and retrying visibility assertions

[Amoifr]

Fixes #199

Both points from the issue:

• Configurable timeout: a default_timeout option (ms) on PlaywrightBrowser, wired to a BROWSER_DEFAULT_TIMEOUT env var in HasBrowser. It is applied via page->setDefaultTimeout(), so it covers actions and the waitUntil*() methods. When not set, Playwright's 30 second default stays as is.
• Retrying assertions: assertVisible()/assertNotVisible() now poll client-side (100ms interval, 5 second cap) through Playwright\Testing\Expect, the same shape as Use auto-waiting locator assertions playwright-php/playwright-symfony#35. Failure messages are unchanged, and both still go through session()->assert() first so exception-page detection keeps working.

Tests: the retry is proven against #timeout-box (visible 500ms after load, asserted without any waitUntil*()), and the timeout by asserting a 250ms configured wait fails well under Playwright's 30s default.

As noted in the issue this makes waitUntilVisible()/waitUntilNotVisible() mostly redundant; I left them untouched, happy to deprecate them here or in a follow-up if you prefer.

[Amoifr]

The two red jobs on the first run were a pre-existing race, not related to this diff: the file-saving tests share the same var/browser/source/source.txt under paratest --functional, so can_save_formatted_json_source and can_save_source_when_exception each read the other's output. I opened #209 with a fix (unique filename per save). Re-triggered CI here in the meantime.