Noop CDP methods that go-rod requires

go-rod appears to stop processing when it receives an error, such as
UnknownMethod. Added placeholder handlers for Network.setUserAgentOverride and
Page.stopLoading.

Setting a custom user agent is something still being discussed, so no-oping it
seems reasonable. And, due to the currently synchronous nature of the initial
page load, no-oping stopLoading also seems reasonable.

https://github.com/lightpanda-io/browser/issues/867

src/cdp/domains/page.zig

@@ -31,6 +31,7 @@ pub fn processMessage(cmd: anytype) !void {
         addScriptToEvaluateOnNewDocument,
         createIsolatedWorld,
         navigate,
+        stopLoading,
     }, cmd.input.action) orelse return error.UnknownMethod;
 
     switch (action) {
@@ -40,6 +41,7 @@ pub fn processMessage(cmd: anytype) !void {
         .addScriptToEvaluateOnNewDocument => return addScriptToEvaluateOnNewDocument(cmd),
         .createIsolatedWorld => return createIsolatedWorld(cmd),
         .navigate => return navigate(cmd),
+        .stopLoading => return cmd.sendResult(null, .{}),
     }
 }