GRT: resistance-aware nets percentage TCL parameter

[jfgava]

Summary

FastRoute (FastRoute.h / FastRoute.cpp):

New member res_aware_nets_percentage_ = 15 (default 15%)
setResAwareNetsPercentage(float) / getResAwareNetsPercentage()

GlobalRouter ([GlobalRouter.h] / [GlobalRouter.cpp]):

setResAwareNetsPercentage(float) declaration + implementation (delegates to fastroute_->setResAwareNetsPercentage)
SWIG ([GlobalRouter.i]):

set_res_aware_nets_percentage(float) wrapper TCL ([GlobalRouter.tcl]):

-res_aware_nets_percentage added to global_route command args and parse_key_args
Handler validates with sta::check_percent and calls grt::set_res_aware_nets_percentage

Usage: global_route -resistance_aware -res_aware_nets_percentage 25 — omitting it defaults to 15%.

Type of Change

• New feature
• Documentation update

Impact

Option to set the percentage of nets to use resistance-aware routing.

Verification

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

[gemini-code-assist]

Code Review

This pull request introduces a new -res_aware_nets_percentage parameter to configure the percentage of resistance-aware nets in global routing, exposing it through Tcl, SWIG, and C++ APIs. The review feedback highlights an inconsistency where the Tcl interface validates the input as a percentage (0-100), but the C++ backend treats it as a fraction (0-1), which would lead to incorrect scaling (e.g., 15% being interpreted as 1500%). To resolve this, the reviewer suggests storing the value as a percentage (0-100) with a default of 15.0, dividing it by 100.0 before passing it to updateSlacks, and updating the documentation to reflect this scale.