dbSta: use public LevelizeObserver API from OpenSTA

[dsengupta0628]

Summary

Switch dbSta's level-change observer over to the newly-exposed OpenSTA public API (sta/LevelizeObserver.hh + Sta::setLevelizeObserver), removing three workarounds that were needed when the observer machinery was internal to OpenSTA.

Cleanup code from #10352 post merge of upstream PR parallaxsw/OpenSTA#433

This is a cleanup PR only; behavior of dbSta::levelizedDrvrVertices() and its cache-invalidation path is identical.

Background

dbSta installs a LevelizeObserver so that its levelized_drvr_vertices_ cache is invalidated whenever the timing graph's vertex levels change. Levelize has a single observer slot, so dbSta's observer replaces the default StaLevelizeObserver that Sta::makeObservers installs. The default observer forwards level-change events to Search and GraphDelayCalc to keep their incremental-update iterators consistent — so dbSta's replacement must preserve that forwarding.

Before this change, doing that required:

1. Adding ${OPENSTA_HOME} and ${OPENSTA_HOME}/include/sta as PRIVATE includes on dbSta_lib to reach search/Levelize.hh (not part of OpenSTA's public include set).
2. Calling levelize_->setObserver(...) directly — levelize_ is protected on StaState, a private contract.
3. Hand-replicating StaLevelizeObserver's Search + GraphDelayCalc forwarding inside DbStaLevelizeObserver. If upstream added new work to StaLevelizeObserver, the dbSta copy would silently drift.

OpenSTA now exposes:

• A public header include/sta/LevelizeObserver.hh containing both LevelizeObserver (interface) and StaLevelizeObserver (default implementation with Search + GraphDelayCalc forwarding).
• A public setter Sta::setLevelizeObserver(LevelizeObserver*) that owns the observer and deletes any prior one.

OpenROAD changes in this PR

src/dbSta/src/dbSta.cc

• Replace #include "search/Levelize.hh" with #include "sta/LevelizeObserver.hh".
• Change DbStaLevelizeObserver to inherit from StaLevelizeObserver instead of the bare LevelizeObserver interface, and chain to the base class methods instead of re-implementing the Search + GraphDelayCalc forwarding by hand
• Use setLevelizeObserver(...) instead of levelize_->setObserver(...).

src/dbSta/src/CMakeLists.txt

• Drop the PRIVATE include hack — no longer needed since the observer header is now in OpenSTA's public include set

Type of Change

• Refactoring

Impact

None. Better maintainability

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).

Related Issues

[Link issues here]

[gemini-code-assist]

Code Review

This pull request refactors DbStaLevelizeObserver to inherit from StaLevelizeObserver instead of LevelizeObserver, delegating the forwarding of level change events to the base class and removing redundant calls. Additionally, it cleans up the build configuration by removing unnecessary private OpenSTA include paths from CMakeLists.txt and updates the includes in dbSta.cc. There are no review comments, and I have no feedback to provide.

[dsengupta0628]

secure CI http://secure-ci:8080/view/My/job/SB/job/secure-or_enhance_drvr_level_to_dbsta/

[dsengupta0628]

Even though the secure-ci shows some secure designs drift QoR, they are unrelated to my change and a separate metric update is already being done with a different PR from @maliberty to update those metrics. So this is okay to merge now

[dsengupta0628]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. What shall we delve into next?

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