dpl: equalize site weight between width and height

[gudeh]

Summary

Currently DPL negotiation legalizer consider the same weight on its cost function for width and height of a site. This does not make sense since they do not have the same dimensions in DBU.

We make moves such as this one, notice the empty space by the lef of the moved instances:

With the current PR they move to the closest available space.

Type of Change

• Bug fix

Impact

We get up to 25% reduction in displacement at stage 3-5 for public designs:

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

The changes in this PR come from #11121

[gemini-code-assist]

Code Review

This pull request refactors the displacement calculation in NegotiationLegalizer to measure displacement in site widths on both axes, ensuring row jumps are priced correctly relative to horizontal site steps. It introduces cached row Y coordinates (row_y_dbu_) and helper methods rowDispInSites and displacementInSites to calculate distances accurately. The metrics, search window logic, and target cost calculations are updated to use these new helpers. There are no review comments, so I have no additional feedback to provide.

[gudeh]

@osamahammad21 you mentioned being worried about changes in displacement. Notice that this function is the same as before, it previously already considered the displacement in sites:

  [[nodiscard]] int displacement() const
  {
    return std::abs(x - init_x) + std::abs(y - init_y);
  }