Fix allocation regressions on Julia 1.12

Replace LinearAlgebra norm/dot/normalize\!/cross with inline scalar
helpers (norm3, dot3, normalize3\!, cross3\!) across hot paths. Unroll
heterogeneous filament loop to eliminate Union dispatch. Fix tuple
slicing, matrix slice copies, and broadcast allocations.

AIC: 4010 → 10 allocs, gamma_loop: 9 → 0, calculate_results: 857 → 590,
solve_base\!/solve\!: broken → passing.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: 1-Bart-1