Modernize and cleanup: Swift 5.9, concurrency safety, and documentation

.github/workflows/ci.yml

@@ -0,0 +1,32 @@
+name: CI
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+    branches: [master]
+
+jobs:
+  build-and-test-macos:
+    runs-on: macos-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Swift version
+        run: swift --version
+      - name: Build
+        run: swift build
+      - name: Test
+        run: swift test
+
+  build-and-test-linux:
+    runs-on: ubuntu-latest
+    container: swift:5.9
+    steps:
+      - uses: actions/checkout@v4
+      - name: Swift version
+        run: swift --version
+      - name: Build
+        run: swift build
+      - name: Test
+        run: swift test
+

Package.swift

@@ -1,11 +1,11 @@
-// swift-tools-version:5.8
+// swift-tools-version:5.9
 
 import PackageDescription
 
 let package = Package(
     name: "XCEPipeline",
     platforms: [
-        .macOS(.v10_15), // depends on Combine
+        .macOS(.v12),
         .iOS(.v15)
     ],
     products: [