Cts: improve level creating threshold

[arthurjolo]

Summary

This PR improves the H-tree level creation stop criterion in CTS by using the actual sink region geometry, preventing shallow trees.

The existing stop criterion for H-tree level creation relied solely on the number of sinks per subregion (isNumberOfSinksTooSmall). This could cause the tree to stop building levels too early or too late, depending on sink distribution — particularly for designs with max_wirelength set or macro trees.

Type of Change

• New feature

Impact

• Combined H-tree level stop criterion: When max_wirelength is set, level creation now stops only when both the largest sink region HPWL is smaller than max_wirelength and the number of sinks per subregion is too small. Previously, the sink-count check alone could stop the tree prematurely when sinks were still geometrically spread out. When max_wirelength is not set, the original sink-count-only criterion is preserved.

• Guard against invalid maxWl (TritonCTS.cpp:247-249): setMaxWl is now only called when resizer_->findMaxWireLength() returns a positive value, preventing a zero/negative max wirelength from disabling the geometric check

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

[gemini-code-assist]

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