Commit the converged material state each time step

History-dependent materials (e.g. J2 plasticity) read their previous converged
state from the "old" qpoint material arrays, but those arrays were only ever
written once, at INITMATERIAL. SolutionSystem::updateMaterialsSolution() (which
copies current -> old) existed but was never called, and formBulkFE(UPDATEMATERIAL)
falls into the generic branch that writes the *current* arrays, not the old ones.
As a result the old material state stayed frozen at its initial value for the
whole simulation.

This is wrong for any non-monotonic/cyclic loading (the material forgets it ever
yielded: no residual plastic strain on unload, no Bauschinger effect); it only
happens to give the right answer for monotonic loading because incremental and
single-step return mapping then coincide. Verified directly: the old plastic
strain read 0 every step while the current grew to 2.3e-2.

Fix: call updateMaterialsSolution() after the step's material update so the
converged state becomes the next step's old state. Non-history materials are
unaffected (their old arrays are never read) - transient diffusion output is
byte-identical and shows no runtime change; plasticity now carries its history
(costs one extra per-step state copy).

Author: yangbai90

src/TimeStepping/TimeSteppingSolve.cpp

@@ -114,7 +114,11 @@ bool TimeStepping::solve(FECell &t_FECell,
                                   t_SolnSystem,
                                   t_EqSystem.m_AMATRIX,
                                   t_EqSystem.m_RHS);
-
+            // commit the converged qpoint material state as the new "old" state, so that
+            // history-dependent materials (e.g. plasticity) carry their state to the next step.
+            // Without this the old state stays frozen at its initial value, which only happens
+            // to give the right answer for monotonic loading.
+            t_SolnSystem.updateMaterialsSolution();
 
             if(t_FECtrlInfo.CurrentStep%t_Output.getIntervalNum()==0){
                 t_ProjSystem.executeProjection(t_FECell,t_DofHandler,t_ElmtSystem,t_MateSystem,t_FE,t_SolnSystem,t_FECtrlInfo);