Model SEIRS-DQ - confinament, reinfeccio i beta(t) (Lab02 bonus)

Extensio del SEIRD (bonus): (1) confinament S->C si I>Ic (rc*S) i contagi residual C->E = rho*beta*C*I/N; (2) reinfeccio R->S = omega*R, omega=1/immunityPeriod; (3) transmissivitat variable beta(t)=beta0*RTF(t) segons variant (Wuhan 1x, Alpha 1.5x, Delta 2x, Omicron 4x) i IFR per variant. Euler dt=0.25, 730 dies.