Add Binance REST client with OHLCV, ticker, and volume methods

Implements BinanceRestClient wrapping python-binance with get_top_coins,
get_ohlcv, get_all_prices, and get_24h_volume. Includes mocked unit tests
for all public methods.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/test_binance_rest.py

@@ -0,0 +1,42 @@
+import pytest
+from unittest.mock import patch, MagicMock
+from data.binance_rest import BinanceRestClient
+
+@pytest.fixture
+def client():
+    with patch("data.binance_rest.Client") as mock_client_cls:
+        mock_client_cls.return_value = MagicMock()
+        c = BinanceRestClient(api_key="test", api_secret="test")
+    return c
+
+def test_get_top_coins_returns_symbols(client):
+    mock_tickers = [
+        {"symbol": "BTCUSDT", "quoteVolume": "1000000"},
+        {"symbol": "ETHUSDT", "quoteVolume": "500000"},
+        {"symbol": "BTCETH", "quoteVolume": "200000"},
+    ]
+    with patch.object(client.client, "get_ticker", return_value=mock_tickers):
+        result = client.get_top_coins(limit=2)
+    assert "BTCUSDT" in result
+    assert "ETHUSDT" in result
+    assert "BTCETH" not in result
+
+def test_get_ohlcv_returns_dataframe(client):
+    mock_klines = [
+        [1700000000000, "40000", "41000", "39000", "40500", "100",
+         1700003599999, "4050000", 500, "50", "2025000", "0"]
+    ]
+    with patch.object(client.client, "get_klines", return_value=mock_klines):
+        df = client.get_ohlcv("BTCUSDT", interval="1h", limit=1)
+    assert len(df) == 1
+    assert "close" in df.columns
+    assert df.iloc[0]["close"] == 40500.0
+
+def test_get_all_tickers(client):
+    mock_prices = [
+        {"symbol": "BTCUSDT", "price": "40000.00"},
+        {"symbol": "ETHUSDT", "price": "3500.00"},
+    ]
+    with patch.object(client.client, "get_all_tickers", return_value=mock_prices):
+        result = client.get_all_prices()
+    assert result["BTCUSDT"] == 40000.0