Pace desktop call video independently and coalesce immediate UI publication

tools/chatgui/tests/test_call_video_clock.cpp

@@ -32,6 +32,7 @@ extern "C" int __wrap_call_video_port_pull(uint64_t id, call_video_frame* out) {
     if (cursor >= (int)frames.size() || nowUs() - start < cursor * 33333ll) return 0;
     const auto& f = frames[cursor]; *out = {}; out->call_id = id; out->format = format;
     out->pts_us = f.pts; out->frame_id = ++cursor; out->flags = f.key ? CALL_VIDEO_KEY : 0;
+    out->received_us = start + (cursor - 1) * 33333ll;
     out->size = out->length = f.data.size(); auto* data = static_cast<uint8_t*>(u_malloc(out->size));
     memcpy(data, f.data.constData(), out->size); out->data = data; return 1;
 }