Add utility functions

Sources/DemoKit/DemoKit.swift

@@ -1,2 +1,20 @@
 // The Swift Programming Language
 // https://docs.swift.org/swift-book
+
+/// A utility structure providing demo functionality
+public struct DemoKit {
+
+    /// Formats a greeting message
+    /// - Parameter name: The name to greet
+    /// - Returns: A formatted greeting string
+    public static func greet(_ name: String) -> String {
+        return "Hello, \(name)! Welcome to DemoKit."
+    }
+
+    /// Calculates the sum of an array of integers
+    /// - Parameter numbers: Array of integers to sum
+    /// - Returns: The sum of all numbers
+    public static func sum(_ numbers: [Int]) -> Int {
+        return numbers.reduce(0, +)
+    }
+}