fix(trader): harden API calls with timeouts, strict balance parsing, error context

- binance/bybit/gate: SDK default http.DefaultClient has no timeout; use a
  dedicated 30s-timeout client so a hung connection cannot stall the loop
- bybit: stop mutating http.DefaultClient.Transport, which leaked the
  referer header into every other HTTP request in the process
- add types.ParseFloatField: empty exchange fields stay zero, but malformed
  numeric values now surface as errors instead of silently becoming zero
  balances (applied to GetBalance across 8 exchanges)
- wrap order/market-data errors in auto_trader_orders and okx cancel paths
  with symbol context; log per-order cancel failures in okx CancelAllOrders

trader/bybit/trader_account.go

@@ -51,19 +51,28 @@ func (t *BybitTrader) GetBalance() (map[string]interface{}, error) {
 
 	if len(list) > 0 {
 		account, _ := list[0].(map[string]interface{})
+		var parseErr error
 		if equityStr, ok := account["totalEquity"].(string); ok {
-			totalEquity, _ = strconv.ParseFloat(equityStr, 64)
+			if totalEquity, parseErr = types.ParseFloatField("totalEquity", equityStr); parseErr != nil {
+				return nil, parseErr
+			}
 		}
 		if availStr, ok := account["totalAvailableBalance"].(string); ok {
-			availableBalance, _ = strconv.ParseFloat(availStr, 64)
+			if availableBalance, parseErr = types.ParseFloatField("totalAvailableBalance", availStr); parseErr != nil {
+				return nil, parseErr
+			}
 		}
 		// Bybit UNIFIED account wallet balance field
 		if walletStr, ok := account["totalWalletBalance"].(string); ok {
-			totalWalletBalance, _ = strconv.ParseFloat(walletStr, 64)
+			if totalWalletBalance, parseErr = types.ParseFloatField("totalWalletBalance", walletStr); parseErr != nil {
+				return nil, parseErr
+			}
 		}
 		// Bybit perpetual contract unrealized PnL
 		if uplStr, ok := account["totalPerpUPL"].(string); ok {
-			totalPerpUPL, _ = strconv.ParseFloat(uplStr, 64)
+			if totalPerpUPL, parseErr = types.ParseFloatField("totalPerpUPL", uplStr); parseErr != nil {
+				return nil, parseErr
+			}
 		}
 	}