fix: preserve BNFCR in zero-balance filter and emit MiCA warning (#74)

* fix: use availableBalance for BNFCR in FutureBalance

For EU/EEA accounts under Binance MiCA Credits Trading Mode, BNFCR
walletBalance can be negative (fees and PnL are charged in BNFCR).
Binance stores the total cross-margin available balance — aggregating
all stablecoins minus used margin — in availableBalance on the BNFCR
asset entry. Using availableBalance as Amount for BNFCR ensures the
BinanceCryptoFutureMarginModel receives the correct collateral figure
and the > 0 guard passes for accounts with sufficient collateral.

* refactor: preserve BNFCR in zero-balance filter, revert availableBalance

- Add BNFCR exception to the zero-balance filter in BinanceBaseRestApiClient
  so BNFCR always passes through even when walletBalance=0
- Remove manual BNFCR injection in BinanceFuturesRestApiClient (no longer needed)
- Revert FutureBalance.Amount to use walletBalance only (availableBalance causes
  double-counting with Lean's own PnL/margin tracking)

* feat: emit BrokerageMessageEvent warning when BNFCR detected in account balances

* fix: update MiCA warning message to reflect all collateral assets

Author: Romazes

QuantConnect.BinanceBrokerage/BinanceBaseRestApiClient.cs

@@ -190,7 +190,7 @@ protected BalanceEntry[] GetCashBalance(string apiPrefix)
             return JsonConvert
                 .DeserializeObject<AccountInformation>(response.Content, CreateAccountConverter())
                 .Balances
-                .Where(s => s.Amount != 0)
+                .Where(s => s.Amount != 0 || s.Asset.Equals("BNFCR", StringComparison.InvariantCultureIgnoreCase))
                 .ToArray();
         }
 

QuantConnect.BinanceBrokerage/BinanceBrokerage.cs

@@ -235,6 +235,13 @@ public override List<CashAmount> GetCashBalance()
             if (balances == null || !balances.Any())
                 return new List<CashAmount>();
 
+            if (balances.Any(b => b.Asset.Equals("BNFCR", StringComparison.InvariantCultureIgnoreCase)))
+            {
+                OnMessage(new BrokerageMessageEvent(BrokerageMessageType.Warning, "BinanceFuturesCreditsTradingMode",
+                    "Binance Futures Credits Trading Mode detected. " +
+                    "Margin will be calculated using all available collateral assets in the account."));
+            }
+
             return balances
                 .Select(b => new CashAmount(b.Amount, b.Asset.LazyToUpper()))
                 .ToList();

QuantConnect.BinanceBrokerage/BinanceFuturesRestApiClient.cs

@@ -100,12 +100,7 @@ public override List<Holding> GetAccountHoldings()
 
         public override BalanceEntry[] GetCashBalance()
         {
-            var balances = GetCashBalance(_prefixV2) ?? [];
-            if (!balances.Any(x => x.Asset.Equals("BNFCR", StringComparison.InvariantCultureIgnoreCase)))
-            {
-                balances = balances.Concat([new FutureBalance() { Asset = "BNFCR", WalletBalance = 0 }]).ToArray();
-            }
-            return balances;
+            return GetCashBalance(_prefixV2) ?? [];
         }
 
         /// <summary>