fix(swift): update Package.swift minimum iOS version to 16.0 for Duration compatibility (#1242)

The Swift SDK uses the Duration type in FliptClient initializer parameters
(requestTimeout and updateInterval), but Duration is only available from
iOS 16.0+. The Package.swift previously declared iOS 13+ support, causing
a version mismatch that prevented installation.

This updates the minimum iOS requirement from 13.0 to 16.0 to align with
Duration type availability. macOS 13.0 already supports Duration, so no
change needed there.

Fixes #1241

Signed-off-by: Mark Phelps <[email protected]>

Author: markphelps

Package.swift

@@ -4,7 +4,7 @@ import PackageDescription
 
 let package = Package(
     name: "FliptClient",
-    platforms: [.iOS(.v13), .macOS(.v13)],
+    platforms: [.iOS(.v16), .macOS(.v13)],
     products: [
         .library(
             name: "FliptClient",