ppl: block regions overlapping pdn wires and obstructions

[eder-matheus]

Summary

place_pins and place_pin ignored boundary power grid geometry, so signal IO
pins were placed on top of or abutting -extend_to_boundary straps and the
power/ground BPins pdngen creates there, causing shorts and spacing violations
found only at detailed route.

Blocking shapes are now padded by the pin footprint plus the required spacing,
applied uniformly to special net wires, via landing pads, routing obstructions
and fixed pins, including shapes within pin reach of the edge. Also fixed while
here: mirrored pins landing on blocked slots, polygon dies ignoring blocked
regions, place_pin unaware of this geometry, width dependent
(PARALLELRUNLENGTH) spacing for wide straps, and MINSPACING/EFFECTIVEWIDTH
attributes being discarded. getBlockedRegionsFromDbObstructions() was dead
code and is now wired in.

Type of Change

• Bug fix

Impact

Slots too close to boundary PDN geometry become unavailable, so IO pin positions
change in designs with boundary PDN (slightly different HPWL). Designs without
it are unaffected — no golden file changes in pre existing tests. A constrained
region fully covered by the power grid now fails with PPL-76/PPL-82 instead of
producing violations.

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).

162/162 ppl tests pass, including 13 new ones. Also verified the place_pins
consumers in gpl, odb, rsz and mpl.

Related Issues

Fixes https://github.com/The-OpenROAD-Project-private/OpenROAD/issues/3655

[gemini-code-assist]

Code Review

This pull request enhances the I/O Placer to respect routing obstructions and Power Delivery Network (PDN) shapes near the die boundary, ensuring proper spacing for placed pins. It introduces caching for pin sizes and layer spacing, updates Hungarian matching to avoid blocked mirrored slots, and refactors getters in Core to return const references. The review feedback focuses on improving code robustness and performance in IOPlacer.cpp, specifically by optimizing map lookups to avoid double lookups or std::out_of_range exceptions, adding null checks for tech_layer and top_grid_, and ensuring non-routing layers are handled correctly.