PyStratify 0.10.4

Every guided mode of a cylinder. A point source beside or inside a lossless cylinder could lose the power it couples into some of the cylinder's guided modes: the mode search dropped real roots (Brent's minimiser stalled just above a fixed |det| bar) while the solve reported convergence. Over 60 random lossless cylinders the totals moved by more than 1e-3 in 28 of 97 comparable cases (up to 9.5%), and 11 cases that raised an error now solve. For a step-index fibre the modes found now equal those of its closed-form dispersion relation.

Found by a new 3D FDTD benchmark against MIT Meep (benchmarks/fdtd_meep.py → FDTD_MEEP.md): Meep converges toward PyStratify to 0.74% at 60 px/µm for every orientation, through a mode cutoff.

Also: near_field is exact at a sphere's centre (Bohren & Huffman's d₁, m c₁), and sphere near fields are benchmarked against scattnlay (≤ 8.2e-13) and treams (≤ 6.6e-14) in benchmarks/mie_codes.py.