Improve soundscript expand reuse and benchmarks

[jakemccloskey]

Summary

• skip empty generated macro expansion rounds when generated output only contains unused macro-looking imports/text
• add repeatable expand benchmark fixtures and reports
• prime builtin annotated/final stages from the previous prepared program so unchanged source files are reused
• compile connected macro module graphs through one prepared program and reuse computed final output text during expand writes

Notes

The real Soundstage benchmark fixture now shows annotated/final rebuilds reusing 89-90 of 91 files; expandMacros remains the next dominant hotspot.