squashInstructionsIntoSourceLines

Legacy helper for an optional source-line grouped view: squashes IR instruction nodes into their owning CodeSourceLine box. The default detailed Cytoscape/Sigma path does not call this; it renders IR nodes directly and keeps source text as tooltip metadata.

Each line view absorbs its instructions' labels into instructionLabels, edges are remapped instruction→line, self-loops are dropped, and parallels are deduped, so the data flow becomes line-to-line.