grt/cugr: support pins above the max routing layer

[eder-matheus]

Summary

global_route -use_cugr aborted (SIGABRT) when a net had a pin above the max
routing layer (bumps, top-metal ports): CUGR's layer universe stops at the
ceiling but pin shapes did not, so selectShapeAccessPoint indexed
layer_directions_ out of bounds. FastRoute routes these designs, so:

• Design::makeNetPins: clamp pin shapes to the top routable layer (plus the
  ROUTING filter the iterm loop already had).
• updatePinAccessPoints: keep a top-metal pin's real connection layer, so
  connectTopLevelPins still stacks the vias above the ceiling.
• CUGR::buildTreeFromRoute: clamp above-ceiling vias instead of rejecting the
  tree, so post-DRT adoption doesn't force a reroute.

Type of Change

• Bug fix

Impact

These designs now route with -use_cugr, with guides matching the FastRoute
baseline. All changed paths are CUGR-only and were unreachable before (the
abort was unconditional), so nothing previously working changes.

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).

Related Issues

None.

[eder-matheus]

@codex review

[gemini-code-assist]

Code Review

This pull request addresses issues where pins sitting above the maximum routing layer would cause CUGR global routing to abort or fail. It introduces layer clamping for pins and vias above the ceiling, ensuring that top-metal pins retain their real layers for proper via stacking while preventing out-of-bounds layer indices. Additionally, a potential null pointer dereference was identified in Design.cpp where bpin_box->getTechLayer() is called without checking if the returned pointer is null.

[chatgpt-codex-connector]

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