[route]

Replaces the (object, index, total) callback shape with a chain of responsibility. Supersedes #701.

• Callbacks run in the order they were added and the rest are skipped once one handles the object: continue, respond or abort for a request, continue or abort for an auth challenge, accept or dismiss for a dialog. A callback that doesn't care just returns.
• An object nobody handled gets a default: a request is continued, an auth challenge gets Chrome's default response, a dialog is accepted with a warning.
• Callbacks receive only the object. page.on(:request, &:continue) works now, it used to call continue(index, total).
• InterceptedRequest#handled?, AuthRequest#handled? and Dialog#handled? tell whether a previous callback took the object.
• Network#authorize and the proxy authorization no longer count callbacks to decide what to do.

Breaking:

• index and total are nil for blocks that still take them, a lambda taking three arguments raises.
• A callback that holds a request to answer later gets it continued.
• A callback registered after the handler no longer sees that request.
• Raw CDP events keep yielding (params, index, total).