Add a reusable pan & zoom controller for the plotting views

Add a reusable pan & zoom controller for the plotting views: a task in MiMo-V2.6-RL-oss: Agentic RL Environments (MiMo RL release). Our VisPy-based views need a small, self-contained controller that owns the pan (2D translation) and zoom (2D scale) state of a scene and keeps any attached GPU…