Gs_rs and Res_gs are @:ALLOCATE'd but never deallocated in the Riemann finalizer #1568

Symptom: one-shot memory leak + dangling GPU mapping per run; violates the project's ALLOCATE/DEALLOCATE pairing rule.

Mechanism: @:ALLOCATE(Gs_rs(1:num_fluids)) (src/simulation/m_riemann_solvers.fpp:3570 on master) and @:ALLOCATE(Res_gs(1:2, 1:Re_size_max)) (:3578) have no matching @:DEALLOCATE in s_finalize_riemann_solvers_module (:4691-4704).

Introduced: Res_gs never had a deallocate (2022 GPU merge, 6def75421, @anandrdbz); Gs_rs lost its deallocate as collateral in #39 (627bf85d0, 2022-12-29, @anshgupta1234) — the original hypoelasticity PR #29 had deallocate(gammas, pi_infs, Gs) and #39 deleted that line while relocating the other two arrays. Tagging @anandrdbz and @anshgupta1234 for context.

Fix: not yet fixed; tracked cleanup (documented in #1556's review notes). A two-line @:DEALLOCATE addition.