IV.D292 — tau-to-SI conversion

The tau-to-SI mass conversion factor is Lambda_M = m_n / m_n^(tau) = 1.674927500(83) x 10^(-27) kg/m.u._tau, where m_n^(tau) = 1 by convention. Once fixed, every other mass follows: m_e = Lambda_M/R, m_p = Lambda_M * (1 - delta_A/m_n).