feat: daily volume top20 rank per exchange in market page

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/test_hub_volume_rank_lib.py

@@ -0,0 +1,43 @@
+from datetime import datetime
+
+from hub_volume_rank_lib import (
+    cache_needs_refresh,
+    format_volume_quote,
+    merge_exchange_rank,
+    rank_date_label,
+)
+
+
+def test_rank_date_label_after_reset():
+    # 2026-06-08 09:00 北京时间 → 昨日交易日 2026-06-07
+    dt = datetime(2026, 6, 8, 9, 0, 0)
+    assert rank_date_label(now=dt, reset_hour=8) == "2026-06-07"
+
+
+def test_rank_date_label_before_reset():
+    # 2026-06-08 07:00 → 当前交易日仍算 2026-06-07，昨日为 2026-06-06
+    dt = datetime(2026, 6, 8, 7, 0, 0)
+    assert rank_date_label(now=dt, reset_hour=8) == "2026-06-06"
+
+
+def test_format_volume_quote():
+    assert format_volume_quote(1_500_000_000) == "1.50B"
+    assert format_volume_quote(2_300_000) == "2.30M"
+    assert format_volume_quote(4500) == "4.50K"
+
+
+def test_cache_needs_refresh_and_merge():
+    cache = {"rank_date": "2026-06-05", "exchanges": {}}
+    assert cache_needs_refresh(cache, expected_rank_date="2026-06-07") is True
+    merged = merge_exchange_rank(
+        cache,
+        "binance",
+        {
+            "ok": True,
+            "rank_date": "2026-06-07",
+            "items": [{"rank": 1, "symbol": "BTC/USDT", "volume_quote": 1.0}],
+            "total_symbols": 100,
+        },
+    )
+    assert merged["exchanges"]["binance"]["items"][0]["symbol"] == "BTC/USDT"
+    assert merged["rank_date"] == "2026-06-07"