fix(data): restore pagination early-break + update test count

Code review on b977c37 flagged: with dataset smaller than limit=1000
(typical Phase 1 case), the loop made an extra HTTP request that
returned duplicate rows. Restored `if len(rows) < limit: break`
after extending. Test assertion adjusted from 2 to 1 calls.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/multi_swarm/data/ohlcv_loader.py

@@ -59,6 +59,8 @@ class OHLCVLoader:
             if not rows:
                 break
             all_rows.extend(rows)
+            if len(rows) < limit:
+                break
             last_ts = rows[-1][0]
             new_since = last_ts + timeframe_ms
             if new_since <= since: