Connect a Browserbase session to Selenium WebDriver

Documented steps

1. Create a Browserbase session; it exposes a `seleniumRemoteUrl` (or seleniumRemoteURL) in the session object.
2. Build a custom RemoteConnection (Python) that injects the required headers `x-bb-api-key: $BROWSERBASE_API_KEY` and `session-id: <session.id>` on every request.
3. Point the driver at the session: `driver = webdriver.Remote(custom_conn, options=webdriver.ChromeOptions())`.
4. Drive normally: `driver.get(url)`, `driver.find_element(...).click()`, `driver.save_screenshot('shot.png')`.
5. ALWAYS call `driver.quit()` when done so the session is ended and stops billing; Browserbase can also reuse the same session via the seleniumRemoteUrl.
6. Official doc: https://docs.browserbase.com/platform/browser/getting-started/using-browser-session