Rework request interception for Zigdom

Zigdom broke request interception. It isn't zigdom specifically, but in zigdom
we properly block the parser when executing a normal (not async, not defer)
script. This does not work well with request interception, because an
intercepted request isn't blocked on HTTP data, it's blocked on a message from
CDP. Generally, neither our Page nor ScriptManager are CDP-aware. And, even if
they were, it would be hard to break out of our parsing and return control to
the CDP server.

To fix this, we expand on the HTTP Client's basic awareness of CDP (via its
extra_socket field). The HTTP client is now able to block until an intercepted
request is continued/aborted/fulfilled. it does this by being able to ask the
CDP client to read/process data.

This does not yet work for intercepted authentication requests.

src/http/Http.zig

@@ -90,12 +90,13 @@ pub fn poll(self: *Http, timeout_ms: u32) Client.PerformStatus {
     };
 }
 
-pub fn monitorSocket(self: *Http, socket: posix.socket_t) void {
-    self.client.extra_socket = socket;
+pub fn addCDPClient(self: *Http, cdp_client: Client.CDPClient) void {
+    std.debug.assert(self.client.cdp_client == null);
+    self.client.cdp_client = cdp_client;
 }
 
-pub fn unmonitorSocket(self: *Http) void {
-    self.client.extra_socket = null;
+pub fn removeCDPClient(self: *Http) void {
+    self.client.cdp_client = null;
 }
 
 pub fn newConnection(self: *Http) !Connection {