Rather then adapting on the transport layer, we adapt the puppeteer CDPSession/Connection and make them look like a CDPConnection. The class assumes that callers create a dedicated CDPSession to be used.

The PuppeteerDevToolsConnection installs a generic '*' event listener on all child sessions to funnel all CDP events into DevTools via CDPConnectionObservers. As pointed out in the code comment, we don't need to recursively listen to 'sessionattached' events on child sessions: Nested sessionattached events are reported on all parent sessions.

While not strictly necessary, PuppeteerDevToolsConnection also uninstalls the CDP event listener when a session gets detached (modulo the root puppeteer CDPSession).