Fixing downloads behavior for use_api=false

[shubh24]

why

Downloads were not working properly in use_api=false mode when using Playwright with CDP (Chrome DevTools Protocol). The browser's default download behavior was not configured, causing downloads to fail or be blocked. This change adds proper CDP configuration to enable downloads, matching the behavior already implemented in the TypeScript version of Stagehand.

what changed

• Added CDP download behavior setup in BROWSERBASE mode after browser connection
• Uses Chrome DevTools Protocol to send Browser.setDownloadBehavior command with:
  • behavior: "allow" to enable downloads
  • downloadPath set to the configured or default path
  • eventsEnabled: true for download event tracking

[shubh24]

This isn't yet tested!

[miguelg719]

A changeset would be great! try uvx changeset

[shubh24]

This isn't yet tested!

Tested now, works for this config!

    config = StagehandConfig(
        env="BROWSERBASE",
        browserbase_session_id=session_id,
        ...
        use_api=False,
    )

[miguelg719]

closes #130