Fix optional arg UB, missing deallocates, missing intent

- Remove case default in f_advance_step that dereferenced absent optional
  args fVel/fPos (undefined behavior when called from EE path with adap_dt)
- Add @:DEALLOCATE for p_send_buff, p_recv_buff, p_send_ids in MPI finalize
- Add intent(in) on lag_num_ts in s_initialize_particles_mpi
- Add intent(in) on nBub, pos, posPrev in s_add_particles_to_transfer_list
- Fix bare 3 -> 3._wp in vel_model=3 force computation

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: sbryngelson

src/simulation/m_bubbles.fpp

@@ -597,17 +597,12 @@ contains
                             do l = 1, num_dims
                                 f_bTemp = f_get_bubble_force(fPos(l), fR, fV, fVel(l), fmass_g, fmass_v, &
                                                              fRe, fRho, cell, l, q_prim_vf)
-                                aTemp(l) = 2._wp*f_bTemp/(fmass_g + fmass_v) - 3*fV*fVel(l)/fR
+                                aTemp(l) = 2._wp*f_bTemp/(fmass_g + fmass_v) - 3._wp*fV*fVel(l)/fR
                             end do
                             do l = 1, num_dims
                                 fVel(l) = fVel(l) + h*aTemp(l)
                                 fPos(l) = fPos(l) + h*fVel(l)
                             end do
-                        case default
-                            do l = 1, num_dims
-                                fVel(l) = fVel(l)
-                                fPos(l) = fPos(l)
-                            end do
                         end select
                     end if
 

src/simulation/m_mpi_proxy.fpp

@@ -87,8 +87,9 @@ contains
         !! @param lag_num_ts Number of stages in time-stepping scheme
     subroutine s_initialize_particles_mpi(lag_num_ts)
 
+        integer, intent(in) :: lag_num_ts
         integer :: i, j, k
-        integer :: real_size, int_size, nReal, lag_num_ts
+        integer :: real_size, int_size, nReal
         integer :: ierr !< Generic flag used to identify and report MPI errors
 
 #ifdef MFC_MPI
@@ -503,8 +504,9 @@ contains
         !!                for communication of initial condition)
     impure subroutine s_add_particles_to_transfer_list(nBub, pos, posPrev)
 
-        real(wp), dimension(:, :) :: pos, posPrev
-        integer :: bubID, nbub
+        integer, intent(in) :: nBub
+        real(wp), dimension(:, :), intent(in) :: pos, posPrev
+        integer :: bubID
         integer :: i, j, k
 
         do k = nidx(3)%beg, nidx(3)%end
@@ -989,6 +991,11 @@ contains
         if (ib) then
             @:DEALLOCATE(ib_buff_send, ib_buff_recv)
         end if
+
+        if (bubbles_lagrange) then
+            @:DEALLOCATE(p_send_buff, p_recv_buff)
+            @:DEALLOCATE(p_send_ids)
+        end if
 #endif
 
     end subroutine s_finalize_mpi_proxy_module