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/Extensions/URL.swift

@@ -0,0 +1,8 @@
+import ArgumentParser
+import Foundation
+
+extension URL {
+    static var projectDirectory: URL { URL(fileURLWithPath: FileManager.default.currentDirectoryPath) }
+    static var parentDirectory: URL { .projectDirectory.deletingLastPathComponent() }
+    static var sdkDirectory: URL { .parentDirectory.appendingPathComponent("matrix-rust-sdk") }
+}