Adds targeted strict concurrency setting (#295)

Bumps package file to 5.9 swift tools

Package.swift

@@ -1,4 +1,4 @@
-// swift-tools-version:5.7
+// swift-tools-version:5.9
 // The swift-tools-version declares the minimum version of Swift required to build this package.
 
 import PackageDescription
@@ -234,3 +234,9 @@ extension PackageDescription.Product {
         .library(name: name, targets: [name])
     }
 }
+
+for target in package.targets {
+  var settings = target.swiftSettings ?? []
+  settings.append(.enableExperimentalFeature("StrictConcurrency=targeted"))
+  target.swiftSettings = settings
+}