fix README.playground for swift 6.2

Sources/SQLyra/DataFrame.swift

@@ -45,7 +45,7 @@ extension PreparedStatement {
         while let row = try row() {
             df.appendEmptyRow()
             for index in (0..<columnCount) {
-                if let value = row[index] {
+                if let value = row.value(at: index) {
                     df.rows[count][index] = valueTransformers[index].transform(value)
                 }
             }

Sources/SQLyra/PreparedStatement.swift

@@ -205,17 +205,28 @@ extension PreparedStatement {
         let statement: PreparedStatement
 
         public subscript(dynamicMember name: String) -> Value? {
-            self[name]
+            value(for: name)
         }
 
         public subscript(columnName: String) -> Value? {
-            statement.columnIndexByName[columnName].flatMap { self[$0] }
+            value(for: columnName)
         }
 
         public subscript(columnIndex: Int) -> Value? {
             statement.value(at: columnIndex)
         }
 
+        public func value(for columnName: String) -> Value? {
+            guard let columnIndex = statement.columnIndexByName[columnName] else {
+                return nil
+            }
+            return value(at: columnIndex)
+        }
+
+        public func value(at columnIndex: Int) -> Value? {
+            statement.value(at: columnIndex)
+        }
+
         public func decode<T>(_ type: T.Type, using decoder: RowDecoder? = nil) throws -> T where T: Decodable {
             try (decoder ?? RowDecoder.default).decode(type, from: self)
         }