initialize

Kicks off, on a background thread, a one-shot probe that renders a trivial diagram (the terminal node BinaryDecisionDiagram.terminalOf true) to determine whether this Graphviz installation can actually produce PNGs; the outcome becomes visible through isReady (once the probe completes) and isAvailable (its result). Call this once at application startup, before any renderAsPNG/ it.unibo.tuprolog.ui.gui.GraphRenderView is expected to work; until the probe completes, isAvailable reports false and isReady reports false. Calling it again restarts the probe.