Wire up real Hyperliquid integration and funding rate API

Replaced the placeholder live node with a proper NautilusTrader
TradingNode that connects to Hyperliquid Testnet using the
official adapter. Added:

- common/hyperliquid_api.py: direct REST calls to Hyperliquid's
  info endpoint for funding rates, predicted fundings, and
  asset contexts
- backtests/run_backtest.py: CLI runner for strategy backtests
- Updated funding_rate_arb.py to fetch real funding rates
  instead of using a hardcoded placeholder
- Added requests to requirements.txt

common/hyperliquid_api.py

@@ -0,0 +1,75 @@
+"""
+Hyperliquid API utilities.
+
+Direct REST calls to Hyperliquid info endpoint for data
+not yet covered by the NautilusTrader adapter (funding rates,
+predicted fundings, asset contexts).
+"""
+import requests
+from typing import Any
+
+
+TESTNET_API = "https://api.hyperliquid-testnet.xyz/info"
+MAINNET_API = "https://api.hyperliquid.xyz/info"
+
+
+def _post(api_url: str, payload: dict) -> Any:
+    resp = requests.post(api_url, json=payload, timeout=10)
+    resp.raise_for_status()
+    return resp.json()
+
+
+def get_asset_contexts(testnet: bool = True) -> list[dict]:
+    """
+    Fetch asset contexts including current funding rates.
+    Returns list of per-asset dicts with keys:
+    funding, openInterest, markPx, oraclePx, premium, dayNtlVlm, etc.
+    """
+    api = TESTNET_API if testnet else MAINNET_API
+    data = _post(api, {"type": "metaAndAssetCtxs"})
+    # data[0] = universe, data[1] = asset contexts
+    if isinstance(data, list) and len(data) >= 2:
+        return data[1]
+    return []
+
+
+def get_funding_rate(asset_name: str, testnet: bool = True) -> float | None:
+    """
+    Get the current funding rate for a specific asset.
+    Funding is paid every 8 hours. Positive = longs pay shorts.
+    """
+    ctxs = get_asset_contexts(testnet=testnet)
+    for ctx in ctxs:
+        if isinstance(ctx, dict) and ctx.get("name") == asset_name.upper():
+            funding_str = ctx.get("funding", "0")
+            return float(funding_str)
+    return None
+
+
+def get_all_funding_rates(testnet: bool = True) -> dict[str, float]:
+    """Get funding rates for all assets on Hyperliquid."""
+    ctxs = get_asset_contexts(testnet=testnet)
+    rates = {}
+    for ctx in ctxs:
+        if isinstance(ctx, dict):
+            name = ctx.get("name", "")
+            funding_str = ctx.get("funding", "0")
+            if name:
+                rates[name] = float(funding_str)
+    return rates
+
+
+def get_predicted_funding(asset_name: str, testnet: bool = True) -> float | None:
+    """
+    Get the predicted funding rate for the next interval.
+    Uses the predictedFundings endpoint.
+    """
+    api = TESTNET_API if testnet else MAINNET_API
+    data = _post(api, {"type": "predictedFundings"})
+    if isinstance(data, list):
+        for item in data:
+            if isinstance(item, dict) and item.get("name") == asset_name.upper():
+                # Return the Hyperliquid-specific prediction
+                predicted = item.get("funding", "0")
+                return float(predicted)
+    return None