Expose paired OSWEC fixed hinge in Python WEC API

[cmccomb]

Summary

• Add WEC.fixed_hinge for the existing OSWEC pitch-hinge dynamics, accepting one hydrodynamic flap, an optional stationary base, world-axis hinge/PTO points, and a configured torsional PTO.
• Return named pitch and PTO histories with positive damping dissipation. The underlying dynamics and hydrodynamic coefficients are unchanged.
• Pair the public interface with canonical irregular OSWEC and published regular Nonhydro_Body MATLAB cases; add focused workflow-dispatch choices for those cases.

Validation

• Local Python API suite and OSWEC standalone checks: 15 passed.
• Local paired replay: canonical OSWEC and Nonhydro_Body both passed.
• Fresh pinned MATLAB R2025b canonical two-body OSWEC and nonhydrodynamic base both passed. The canonical run's maximum flap errors over 4,001 samples were 10.0 mm surge, 1.66 mm heave, 0.00201 rad pitch, and 35.6 N m PTO torque; the fixed base was exact.
• The repeat canonical run passed the added public surge/heave/velocity gates.

Scope

This exposes the already supported pure-pitch fixed-hinge layout for regular and PM waves. General Simscape joints and off-axis hinge geometry remain outside this interface.