Automatically open a PR to bump the calver (#4167)

* Update our tools package to Swift 6.1

Also improves the package layout with subdirectories 📁

* Update GenerateSDKMocks to be an Async command.

* Add a tool to bump the project CalVer every month.

* Add a workflow to automatically bump the calendar version.

Note: This only does year & month, the patch is handled by the release script.

Tools/Sources/Commands/UnusedStrings.swift

@@ -0,0 +1,34 @@
+import ArgumentParser
+import CommandLineTools
+import Foundation
+
+struct UnusedStrings: ParsableCommand {
+    static let configuration = CommandConfiguration(abstract: "Generates a report showing which strings aren't used in the project.")
+    
+    @Flag(help: "Save the results to disk instead of printing them.")
+    var saveToFile = false
+
+    func run() throws {
+        try peripheryScan()
+    }
+
+    func peripheryScan() throws {
+        print("Analysing project, this may take a while…")
+        
+        // Uses the existing .periphery.yml with small tweaks to the output.
+        let command = "periphery scan --quiet --relative-results --report-include ElementX/Sources/Generated/Strings.swift"
+        let output = try Zsh.run(command: command)
+        
+        guard let output else {
+            print("Nothing reported.")
+            return
+        }
+        
+        if saveToFile {
+            try output.write(to: .projectDirectory.appending(component: "Unused Strings.txt"), atomically: true, encoding: .utf8)
+            print("Report saved: Unused Strings.txt")
+        } else {
+            print(output)
+        }
+    }
+}