Refactor FuturesBot and SpotBot to utilize ticker enum for candle retrieval

- Updated GetCurrentCandleForPositionClose method in both FuturesBot and SpotBot to parse the ticker parameter into an enum, enhancing type safety and clarity.
- Adjusted TradingBotBase to use the position's ticker for candle retrieval, ensuring consistency across trading bot implementations.

src/Managing.Application/Bots/SpotBot.cs

@@ -143,8 +143,10 @@ public class SpotBot : TradingBotBase
     protected override async Task<Candle> GetCurrentCandleForPositionClose(Account account, string ticker)
     {
         // For live trading, get real-time candle from exchange
+        // ticker parameter is a string representation of the position's ticker
+        var tickerEnum = Enum.Parse<Ticker>(ticker);
         return await ServiceScopeHelpers.WithScopedService<IExchangeService, Candle>(_scopeFactory,
-            async exchangeService => await exchangeService.GetCandle(Account, Config.Ticker, DateTime.UtcNow));
+            async exchangeService => await exchangeService.GetCandle(Account, tickerEnum, DateTime.UtcNow));
     }
 
     protected override async Task<bool> CheckBrokerPositions()