feat: Add Double Pendulum physics example with Verlet Integration

[bryanhoffman]

This PR introduces a new educational example for the "Math and Physics" section. It demonstrates a Double Pendulum using Verlet Integration, offering a more stable and physically accurate alternative to standard Euler-based simulations.

Technical Implementation:

Integration: Uses Position-Based Dynamics (Verlet) for increased numerical stability.

Constraint Solver: Implements a Gauss-Seidel relaxation loop (15 iterations) to maintain rigid rod lengths.

Energy Management: Includes a stochastic Hamiltonian preservation factor. This counteracts numerical damping and simulates a "driven" system (similar to a pendulum on a rickety train), ensuring the system explores its full phase space without losing kinetic energy.

[bryanhoffman]

I wanted to try and create an example for the p5.js website. I hope this example is worthy of publishing, but if it is not, I'd love the feedback to get it there.