gui_toolkit 0.56.0

Added

• Timelines: tools/cdp.mjs record --timeline <dir> keeps a run whole (each action with when it happened, a picture after it, every frame's time), as a page that stands alone, a timeline.json and a Chrome trace; play <timeline.json> --timeline <dir> runs it again, --realtime with its pauses, and fails if a picture differs. tools/timeline.mjs for scripts. Toolkit.frames and Toolkit.pollRecording feed it.
• Page.startScreencast: the window's frames as events, one at a time, limited in rate, none at rest; tools/cdp.mjs cast <dir>.