rcx: add multi-chip extraction pass skeleton

[AcKoucher]

Summary

I'm opening this PR so that we have a place to store the extraction rules file paths. Look at this comment and its PR for more context.

Two new classes:

• Ext::MultiChipExtractor will create parasitics objects inside ODB for all chips and inter-chip bonds.
• Ext::MultiChipSpefWriter will write one SPEF for each chip and one SPEF for each bond based on the parasitics objects inside ODB.

Type of Change

• Skeleton of a future feature.

Impact

None.

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

#11005

[gemini-code-assist]

Code Review

This pull request introduces initial infrastructure for multi-chip (3D) extraction and SPEF writing by adding the MultiChipExtractor and MultiChipSpefWriter classes, integrating them into the Ext class, and dispatching to them when a hierarchical chip is detected. The review feedback identifies critical safety issues where a null top_chip could lead to a null pointer dereference and application crash in ext.i. Additionally, it is recommended to pass ExtractOptions by const reference in extractMultiChip to avoid unnecessary copying.