Replace the readMarketingVersion method with a cleaner Yams based one and extract it into the shared tools

Tools/Sources/Commands/CI/CI.swift

@@ -1,6 +1,7 @@
 import ArgumentParser
 import Foundation
 import Subprocess
+import Yams
 
 struct CI: ParsableCommand {
     static let configuration = CommandConfiguration(abstract: "CI workflow commands that can be run both locally and in CI environments.",
@@ -13,6 +14,19 @@ struct CI: ParsableCommand {
     
     static let testOutputDirectory = "test_output"
     
+    /// Reads the `MARKETING_VERSION` from `project.yml`.
+    static func readMarketingVersion() throws -> String {
+        let projectURL = URL.projectDirectory.appending(component: "project.yml")
+        let projectString = try String(contentsOf: projectURL)
+        
+        guard let projectConfig = try Yams.compose(yaml: projectString),
+              let version = projectConfig["settings"]?["MARKETING_VERSION"]?.string else {
+            throw ValidationError("Could not find MARKETING_VERSION in project.yml.")
+        }
+        
+        return version
+    }
+    
     // MARK: - Linting
     
     /// Runs SwiftFormat in lint mode against the current directory.