pad: reorganize RDLRoute into per net to allow to better route continuity checking

[gadfort]

Summary

This moves all the routing segments into a single net object to allow to better checking of route completeness. Before is a route contained 3 or more bumps, one of the segments would be unrouted. This ensures we check the net continuity before continuing.
There is some testing noise because this removes a redundant segment and changes the order of routing slightly.

Type of Change

• Bug fix
• Refactoring

Impact

Complete routes on daisychained bumps

Verification

• I have verified that the local build succeeds (./etc/Build.sh).
• I have run the relevant tests and they pass.
• My code follows the repository's formatting guidelines.
• I have included tests to prevent regressions.
• I have signed my commits (DCO).

[gemini-code-assist]

Code Review

This pull request refactors the RDL router by splitting the RDLRoute class into RDLNet (representing a net) and RDLSegment (representing individual routing segments), updating the router, GUI, and tests accordingly. The review feedback highlights a potential crash in RDLNet::finalizeSegments() if segments_ is empty, a logical bug in RDLSegment::getUnroutedTerminals() that incorrectly reports all terminals as unrouted, and an optimization opportunity in RDLNet::isRouted() to include a fast-path check and prevent redundant recursive calls.