Pair imported wave paths with archived MATLAB fixtures

[cmccomb]

Summary

Run the production WaveClass against the repository's archived MATLAB-generated imported-wave fixtures. Both .txt and .mat paths now gate imported elevation interpolation and startup ramping over 400 s, plus imported spectral bins, phases, and synthesized elevation over 200 s.

These historical fixtures add a numerical regression check for the import paths. They are not a new comparison to the currently pinned WEC-Sim revision, so published-case badges do not change.

Verification

• Focused tests: 4 passed.
• Full local Python suite: 267 passed, 333 skipped; combined line-and-branch coverage rose from 78.25% to 78.29%, still displayed as 78%.
• Maximum imported-elevation history difference: 1.55e-13 m; maximum imported-spectrum elevation difference: 2.85e-14 m, below 2e-12 m and 1e-12 m gates.