exceptions

HUGR builder exceptions.

Exceptions

MismatchedExit(src)	Edge to exit block signature mismatch.
NoSiblingAncestor(src, tgt)	No sibling ancestor of target for valid inter-graph edge.
NotInSameCfg(src, tgt)	Source and target nodes are not in the same CFG.
ParentBeforeChild	Parent added before child.