Two new algorithms

1- ComputeRotation —> [[simulation.observable]]

• Updates system.phi at every compute step
• Handles three methods via theta_T convention:
  • 0.0 → Integral (relay every step)
  • π → Euler (compare to initial frame)
  • any other value → Threshold (relay when rotation exceeds theta_T)
• Internal state (R0, R_ref, phi_acc) kept in RotationState, one per chain

2- StorePhiTrajectories —> [[simulation.output]]

• Reads system.phi and writes to disk on its scheduler
• One file per theta_T per chain: chains/1/phitrajectories_k.dat

Key design decisions

• system.phi added to Molecules struct right after position — rotation vectors live on the system like positions
• New [[simulation.observable]] TOML section for non-output algorithms
• Parallelizes across chains using Transducers.Map, following the same pattern as Arianna's Metropolis algorithm

TOML usage

[[simulation.observable]]
algorithm = "ComputeRotation"
scheduler_params = {linear_interval = 1}
parameters = {theta_T = [0.0, 0.7854, 3.1416]}

[[simulation.output]]
algorithm = "StorePhiTrajectories"
scheduler_params = {linear_interval = 1, log_base = 2.0}

Note: depends on TheDisorderedOrganization/Arianna.jl#87