feat: add init script

[ling0x]

Fixes #205

The existing evaluate_on_new_document method already provides the functionality of Playwright’s addInitScript, injecting JavaScript before any page scripts load. This method maps directly to Chrome DevTools Protocol’s Page.addScriptToEvaluateOnNewDocument command.

Although different tools use different names, Playwright calls it addInitScript, Puppeteer uses evaluateOnNewDocument, they all achieve the same goal: running initialization scripts ahead of page execution (e.g., to hide navigator.webdriver).

Added:

• Expanded documentation and example for evaluate_on_new_document and add_init_script.
• add_init_script added as an alias for evaluate_on_new_document for better discoverability.

[Sytten]

Seems reasonable to me, I just want to start adding integration tests before expanding the API further to reduce maintenance burden.

[Sytten]

Thanks! Running the test and will merge once it passes.