Waveform navigation edges and HDL event edges are different APIs

When adapting a waveform reader to an HDL causal tracer, do not map posedge directly to a navigation command that only searches for a new value of 1. HDL edge semantics also include 0 to X/Z, and negedge includes 1 to X/Z. Any-change is not equivalent to both event edges because X to Z is neither. A unit fixture provider with correct semantics can hide this adapter bug. Test identical transition sequences through the real provider adapter and the fixture provider; preserve UI rise/fall behavior under separate API modes.