RSZ: repair design reroute for slew fix

[jfgava]

Summary

Wire resistance impact on timing is increasing for advanced nodes. In these PDKs, resistance-aware routing can improve delay significantly. Lower RC constants mean faster signal transitions, which cascades into better hold/setup slack at downstream endpoints and reduces slew-induced noise. The rerouting also reduces the need for buffers and upsizing which avoids inflating the netlist, preserving area and power budgets.

New unit test for the -reroute parameter.

Type of Change

• New feature

Impact

New experimental option (-reroute) for repair_design post-GRT to repair slew violations with resistance-aware rerouting.

Up to 90% reduction in the number of buffers inserted to repair slew violations on some large designs for private PDKs.

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 introduces an experimental -reroute option to the repair_design command, enabling resistance-aware wire rerouting to fix slew violations post-global routing before resorting to driver resizing or buffer insertion. Feedback on the implementation suggests enhancing the robustness of tryRerouteNet by respecting dont_touch constraints on both the net and driver pin, ensuring rerouting is only attempted when the parasitics source is set to global routing, and adding a defensive check to prevent negative values for estimated resistance from skewing the reduction ratio calculation.