[gen] Relax insert edge restrict

[ShaleXIONG]

This pull relaxes the restrict to the insert edges such as ISB.

• Remove the restrict in cycle.ml when insert edges must be adjacent by an external edge, for all diy* tools. This allowed cycle like PodWR ISB PosRR Fre PodWR Fre. Previously no tests will be generated with a warning on the ISB insert edge.
• Remove internal filter restriction. Given two composite relaxations, $R_1$ and $R_2$, the filter now only check the last NON-insert edge in $R_1$ against the first NON-insert edge in $R_2$. In the case, those edges does not exists, it will check the first edge in $R_1$ and last edges in $R_2$. The latter behaviour derives from previous existing behaviour. For example if we have a safe or relax edge [DpAddr ISB], the filter will ignore the ISB but use DpAddr in the filtering process.