Speed up --profile-memory with one memory read per credential

Reuse each credential's post-PUT memory reading as the baseline for the
next, halving the memory-applet SELECTs (each triggers a garbage
collection). A 34-credential profiling run now completes in seconds.

apex_otp_import.py

@@ -707,12 +707,14 @@ def main(argv=None):
 
     # 6. Import.
     policy = ConflictPolicy(args)
-    writer = uid = batch = None
+    writer = uid = batch = ms = None
     memlog_fh = None
+    prev_avail = None
     if args.profile_memory:
         uid = get_uid(connection)
         ms = MemorySession(channel)
-        ms.select()
+        m = ms.select()
+        prev_avail = m["available_persistent"] if m else None
         batch = ms.batch()
         _reauth(oath, pw)
         new_file = not os.path.exists(args.memlog)
@@ -731,13 +733,14 @@ def main(argv=None):
                 continue
             try:
                 if args.profile_memory:
-                    before = MemorySession(channel).available()
-                    _reauth(oath, pw)
                     oath.put(c)
-                    after = MemorySession(channel).available()
-                    _reauth(oath, pw)
-                    consumed = (before - after) if (before is not None
-                                                    and after is not None) else ""
+                    cur = ms.available()          # SELECT memory (GC) -> deselects OATH
+                    _reauth(oath, pw)             # re-select OATH for the next PUT
+                    if prev_avail is not None and cur is not None:
+                        before, after, consumed = prev_avail, cur, prev_avail - cur
+                        prev_avail = cur
+                    else:
+                        before = after = consumed = ""
                     writer.writerow([datetime.datetime.now().isoformat(timespec="seconds"),
                                      uid, batch, c.cred_id, before, after, consumed])
                     print(f"  ok     {c.cred_id}  (consumed ~{consumed} B)")