fix: add preferred number of levels option

[antoneri]

Summary

• add --preferred-number-of-levels N as a soft hierarchy-depth preference for the CLI and public wrappers
• reject the invalid combination with --two-level
• select the best discovered hierarchy by combining hierarchical codelength with the requested level distance without changing the optimization objective

Details

• expose the new option in C++, Python, and JS
• keep behavior unchanged when the option is not used
• regenerate tracked Python SWIG outputs and JS parameter metadata
• add native, Python, and JS coverage for parsing, wrapper serialization, and hierarchy selection

Verification

• make build-native OPENMP=0
• make test-native OPENMP=0
• make build-python-swig OPENMP=0
• make build-python OPENMP=0 (in a local venv)
• make test-python OPENMP=0 (in a local venv)
• make test-python-swig-freshness OPENMP=0 (in a local venv)
• npm ci
• make build-js-metadata OPENMP=0
• make test-js-metadata OPENMP=0
• make test-js OPENMP=0

Closes #308