Reduce OSWEC regular wave tests from 1000s to 240s

- Reduce test_oswec_reg_waves.cpp simulation duration (1000s → 240s)
- Fix floating point loop termination bug (same as sphere fix)
- Rewrite compare_oswec_reg_waves.py to match sphere pattern
- Trim 16 reference data files to 240s (8004 lines each)

Test runtime reduced from ~155s to ~36s (~4x faster).
All 16 wave conditions pass with L2 norms < 1e-7.

All regression tests now passing.

Author: dav-og