Add browser_type / executable_path to MarkdownifyWebScraperDriver

[feder-cr]

fetch_url was hardcoded to p.chromium.launch(headless=True), so there was no way to point it at a different engine or a custom binary. Adds browser_type (defaults to 'chromium', unchanged behavior) and executable_path fields, following the attrs field pattern already used here. Motivated by invisible_playwright, a Playwright wrapper around a Firefox build patched at the source level for a realistic fingerprint, useful for scrapes that hit bot detection on the default Chromium path. Opened as draft, happy to adjust naming or add a test.

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...vers/web_scraper/markdownify_web_scraper_driver.py	66.66%	1 Missing and 1 partial ⚠️

📢 Thoughts on this report? Let us know!

[collindutter]

Thanks! Can you please add some unit tests?