dpl: check edge spacing DRC on opt_mirror

[gadfort]

Summary

optimize_mirror was missing the check on edge spacing rules, this wires in the check.
Note this was generated by Claude, but verified on my failing PDK

Type of Change

• Bug fix

Impact

Fix detail placement invalid cell placements

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

[Link issues here]

[gemini-code-assist]

Code Review

This pull request integrates LEF58 cell edge spacing rule checks into the mirroring optimization process. It updates the OptimizeMirroring class to accept and utilize Network, Grid, and PlacementDRC engines to verify if mirroring a cell would violate edge spacing rules, rejecting candidates that do. A new test case mirror_edge_spacing is also added to verify this behavior. The feedback suggests adding safety checks for network_ and grid_ pointers in isEdgeSpacingLegal to prevent potential null pointer dereferences, as these pointers can be null when edge spacing checks are skipped.