Aerosol3D 0.2.0

Added

• MIE solver integration — New solver="MIE" option in solve_optics() using PyMieScatt
  for spherical particles. MIE theory provides exact optical properties (Q_ext, Q_sca, Q_abs, g, P11)
  for comparison and validation against DDA.
• solver field added to OpticalResult dataclass for result provenance tracking.
• equivalent_diameter and effective_refractive_index properties added to AerosolParticle
  class for solver-agnostic particle characterization.
• DDA orientational averaging via Fibonacci sphere sampling. Averages cross-sections and
  phase function over multiple incident directions.
• compute_legendre_moments() for expanding phase functions into Legendre polynomial coefficients.
• validate_mie_vs_dda.py example script for comparing MIE and DDA results.
• validate_grid_convergence.py example script for demonstrating DDA grid convergence.

Fixed

• DDA asymmetry parameter g — Corrected spherical quadrature weights in _spherical_grid().
  Weights were incorrectly proportional to sin(theta), vanishing at the forward scattering
  direction and causing ~95% error in g. Now uses constant solid-angle weights
  dOmega = d(cos theta) * dphi for the uniform cos(theta) grid.
• DDA scattering angle computation — compute_asymmetry_parameter() now uses
  dot(k_inc, k_scat) instead of the polar angle from the z-axis, fixing g for non-z-axis
  incident directions.
• DDA orientational averaging for g — _orientational_average() now averages g
  arithmetically across orientations instead of recomputing from lab-frame P11 (which is
  isotropic by construction, yielding g ~ 0).
• P11 phase function normalization — _compute_phase_function() now normalizes P11
  by C_sca so that the integral over the full sphere equals 1, matching MIE theory convention.
• n_dirs=1 no longer crashes Fibonacci sphere generation.

Changed

• solve_optics() now accepts explicit solver="MIE" or solver="DDA" parameter.