bug: tau_Re_vf memory leak in Cartesian viscous runs (dealloc only under cyl_coord)

[sbryngelson]

Summary

In src/simulation/m_rhs.fpp, tau_Re_vf is allocated inside if (viscous) but deallocated only when cyl_coord is also true:

! Allocation (inside if (viscous)):
@:ALLOCATE(tau_Re_vf(1:sys_size))
do i = 1, Re_size(1)
    @:ALLOCATE(tau_Re_vf(eqn_idx%cont%end + i)%sf(...))
end do
@:ALLOCATE(tau_Re_vf(eqn_idx%E)%sf(...))

! Deallocation (inside if (cyl_coord)):
if (cyl_coord) then
    do i = 1, num_dims
        @:DEALLOCATE(tau_re_vf(eqn_idx%cont%end + i)%sf)
    end do
    @:DEALLOCATE(tau_re_vf(eqn_idx%E)%sf)
    @:DEALLOCATE(tau_re_vf)
end if

Any run with viscous = .true. and cyl_coord = .false. (i.e., every Cartesian viscous simulation) leaks all tau_Re_vf GPU and host allocations. Violates the @:ALLOCATE/@:DEALLOCATE pairing rule.

Fix

The deallocation guard should be if (viscous), not if (cyl_coord). The number of sf sub-arrays to free mirrors the allocation loop (one per viscous fluid, plus the energy slot).

Discovered

Found during review of PR #1365. Pre-existing in master.