perf: validate retained static and spectral routes

[audunarn]

Summary

• retain the actual ANYstructure runtime context for repeated static work
• add a bounded modal/buckling benchmark with wall, CPU, RSS, matrix, factor, cache, and scientific-consistency reporting
• document the accepted spectral optimizations and measured complete-route results

Validation

• benchmark enforces exact requested mode count and repetition consistency
• actual adapter exercised against candidate ANYsolver source and isolated wheels
• qualified element mechanics and application defaults unchanged

Depends on audunarn/ANYsolver#50. No version bump or publication.