Implement session cache upgrade phase 1 foundation

MLXServerTests/Server/CancellationTokenTests.swift

@@ -0,0 +1,18 @@
+import XCTest
+@testable import MLX_Server
+
+final class CancellationTokenTests: XCTestCase {
+    func testStartsNotCancelled() {
+        let token = CancellationToken()
+
+        XCTAssertFalse(token.isCancelled)
+    }
+
+    func testCancelSetsFlag() {
+        let token = CancellationToken()
+
+        token.cancel()
+
+        XCTAssertTrue(token.isCancelled)
+    }
+}