Pre-allocate workspace buffers as class members to remove ~8M malloc/free
pairs per Newton iteration from LineRelax, ThomasAlgorithm, JFD_times_dv,
J_times_dv, chebft_Zeros, fourft, Derivatives_AB3, and F_of_v.
Rewrite ThomasAlgorithm to operate in-place on input arrays.
Results are bit-identical; no algorithmic changes.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>