Investigate preservation of order edges between gates

#1836 should have fixed the order edge preservation. However, order edges between gates are uncommon, and it is not easy to spot potential bugs. We should deep test everything.

Seems that substitution as [`CY`](https://github.com/Quantinuum/tket2/blob/f8309ac6171d851ef114d780f5e39d6a37630bb4/tket/src/modifier/modifier_resolver/tket_op_modify.rs#L175) may lose some order edges.