Fix: Prevent consecutive operator input in CalculatorModal (#3359)

* Fix: Prevent consecutive operator input in CalculatorModal

Resolved an issue in the CalculatorModal where consecutive operators could be added, resulting in invalid expressions.

- Updated the handleOperator function to ensure only one operator is added at a time.
- Replaced the last operator if a new operator is pressed.
- Ensured the input behaves like a standard calculator.

This change improves the user experience by preventing invalid expressions and aligning the calculator's behavior with user expectations.

* Fix: Ensure proper handling of consecutive operators in CalculatorModal

* Fix: Correct Detekt style issues in CalculatorModal.kt

temp/legacy-code/src/main/java/com/ivy/legacy/legacy/ui/theme/modal/edit/CalculatorModal.kt

@@ -117,31 +117,31 @@ fun BoxWithConstraintsScope.CalculatorModal(
                     text = "÷",
                     testTag = "key_/"
                 ) {
-                    expression += "÷"
+                    expression = handleOperator(expression, "÷")
                 }
             },
             FirstRowExtra = {
                 KeypadCircleButton(
                     text = "×",
                     testTag = "key_*"
                 ) {
-                    expression += "×"
+                    expression = handleOperator(expression, "×")
                 }
             },
             SecondRowExtra = {
                 KeypadCircleButton(
                     text = "−",
                     testTag = "key_-"
                 ) {
-                    expression += "−"
+                    expression = handleOperator(expression, "−")
                 }
             },
             ThirdRowExtra = {
                 KeypadCircleButton(
                     text = "+",
                     testTag = "key_+"
                 ) {
-                    expression += "+"
+                    expression = handleOperator(expression, "+")
                 }
             },
             FourthRowExtra = {
@@ -179,6 +179,19 @@ fun BoxWithConstraintsScope.CalculatorModal(
     }
 }
 
+private fun handleOperator(expression: String, operator: String): String {
+    return if (expression.isNotEmpty() && expression.last().isOperator()) {
+        expression.dropLast(1) + operator
+    } else {
+        expression + operator
+    }
+}
+
+fun Char.isOperator(): Boolean = when (this) {
+    '+', '−', '×', '÷' -> true
+    else -> false
+}
+
 private fun formatExpression(expression: String, currency: String): String {
     var formattedExpression = expression