When done rebuilding, report the number cells and multipoles built as well as...

When done rebuilding, report the number cells and multipoles built as well as the memory required for them.

src/engine.c

@@ -2084,6 +2084,23 @@ void engine_rebuild(struct engine *e, int repartitioned,
   /* Re-build the space. */
   space_rebuild(e->s, repartitioned, e->verbose);
 
+  /* Report the number of cells and memory */
+  if (e->verbose)
+    message(
+        "Nr. of top-level cells: %d Nr. of local cells: %d memory use: %zd MB.",
+        e->s->nr_cells, e->s->tot_cells,
+        (e->s->nr_cells + e->s->tot_cells) * sizeof(struct cell) /
+            (1024 * 1024));
+
+  /* Report the number of multipoles and memory */
+  if (e->verbose && (e->policy & engine_policy_self_gravity))
+    message(
+        "Nr. of top-level mpoles: %d Nr. of local mpoles: %d memory use: %zd "
+        "MB.",
+        e->s->nr_cells, e->s->tot_cells,
+        (e->s->nr_cells + e->s->tot_cells) * sizeof(struct gravity_tensors) /
+            (1024 * 1024));
+
   const ticks tic2 = getticks();
 
   /* Update the global counters of particles */