Changelog

• Fixed GPU path crash on assemblies with <4 bodies when PyTorch batch dim collapsed to scalar
• Fixed SimResult.n_revolutions being off by one timestep
• export_svg() now accepts tooth_style dict for per-render CSS overrides
• Improved error message when BevelPair receives two gears on the same shaft

⚠ Breaking: shaft_histories → shafts; Assembly.add_bevel() removed; Python 3.10+ required.

• GPU-accelerated RK4 via PyTorch (device="gpu"); falls back to CPU gracefully
• Rewritten constraint API — jacobian() is now optional, auto-differentiated via JAX or finite difference
• Per-gear backlash parameter on add_gear()
• New exceptions: OverdeterminedError, UnderdeterminedError, TopologyError
• Newton solver convergence messages include constraint name and residual norm

• Verlet integrator energy drift fix — was accumulating ~0.4% error per 1000 steps
• PivotConstraint.fixed_angle parameter added
• SVG export: show_contact_points option
• Windows wheel for Python 3.12 added to PyPI

⚠ Breaking: simulation core rewritten in Rust; simulate() return type changed to SimResult.

• Rust extension via PyO3 — 8× speedup over NumPy baseline
• Pre-allocated history buffers (no more list-of-dicts)
• Adaptive RK4 with relative/absolute tolerance control
• record_contacts flag for diagnostic contact force logging

• BeltDrive class for chain and belt transmissions
• BevelPair for right-angle and arbitrary-angle bevel meshes
• Structured exception hierarchy replacing bare RuntimeError
• JSON timeseries export via result.export_json()

• History storage switched from list-of-dicts to pre-allocated arrays — 40× memory reduction
• SVG animation uses animateTransform (no JavaScript) for better compatibility
• Fixed pitch circle radius calculation for non-standard module values

• Initial release — spur gear assemblies, RK4 integrator, SVG export
• PyPI wheel for Linux and macOS