[chore]: Refactor getMarketNews in StockService

[0PrashantYadav0]

Description

• Detailed Description:
  The method getMarketNews redundantly checks if a symbol is provided, but the URL constructed is the same regardless of whether the symbol is empty. This redundancy adds unnecessary complexity.
• How to Solve:
  1. Simplify the Method:
     Remove the conditional and always use the same URL format if no special handling is required:

     public String getMarketNews(String symbol) {
         return scheduleApiRequest(() -> {
             String url = String.format("https://finnhub.io/api/v1/news?category=general&token=%s", FINNHUB_API_KEY);
             return makeFinnhubApiRequest(url);
         });
     }

  2. Test for Consistency:
     Verify that the method behaves as expected and that the response remains unchanged.