grt/cugr: scope incremental global routing to dirty nets

[eder-matheus]

Summary

Makes CUGR's incremental global routing actually incremental. Previously each
incremental update reprocessed the full netlist (rebuilt the whole route map,
re-estimated global parasitics, re-scanned congestion, and refreshed every
net's slack/res-aware/pin state). This PR scopes that work to the dirty nets,
matching FastRoute's incremental model:

• Reroute only what changed: a dirty net is rerouted only if it is
  res-aware (rsz-requested), has no route yet (new or journal-restored), or a
  pin moved to a different gcell; otherwise its existing route is kept.
• Patch, don't rebuild: only the nets CUGR actually rerouted
  (getReroutedNets()) are patched into routes_, instead of rebuilding the
  full route map from getRoutes().
• Scope auxiliary updates: slack refresh, res-aware marking, and pin
  access-point sync run over the dirty/rerouted subset only; the global
  parasitics re-estimate and the pattern/maze global congestion scan are
  skipped during incremental passes.
• Share the stage sequence between full and incremental routing so both
  paths stay in lock-step.
• Surface residual congestion: warn once (GRT-128) when an incremental
  pass leaves congestion, since CUGR incremental does not recover congestion it
  induces on neighboring nets.
• Robustness: a no-op incremental pass now clears the rerouted-net list so
  stale entries (possibly naming since-deleted nets) are never replayed by
  getReroutedNets() consumers.

All changes are gated on use_cugr_; the FastRoute path is untouched. This is
the second PR of a stacked series building out CUGR incremental routing.

Type of Change

• Bug fix
• Refactoring

Impact

Faster incremental global routing under CUGR (work is proportional to the dirty
set rather than the whole design) with equivalent routing results. Fixes a
crash where a no-op incremental pass could replay a stale/deleted net. Adds a
GRT-128 warning when incremental routing leaves congestion. No effect on the
FastRoute path.

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 signed my commits (DCO).

[eder-matheus]

@codex review

[gemini-code-assist]

Code Review

This pull request optimizes and refactors the incremental global routing flow in CUGR. Key changes include scoping slack updates, congestion checks, and pin access point updates specifically to the rerouted/dirty nets instead of performing global operations. Additionally, a warning mechanism is introduced to report residual congestion at the end of incremental routing sessions, and the incremental routing flow is streamlined to avoid redundant routing passes. There are no review comments, so no further feedback is provided.

[chatgpt-codex-connector]

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