refactor: remove legacy fallback for device_time

Removes the legacy fallback mechanism in the `device_time` extension that relied on `UnknownMethodException` and `GET_DEVICE_TIME_GET` / `GET_DEVICE_TIME_POST` commands. It now directly uses `execute_script('mobile: getDeviceTime')`. Cleans up unneeded imports, constants, and the `CanRememberExtensionPresence` mixin. Updated the associated tests to remove obsolete HTTP mocks.

Additionally fixes CI failures by pinning the flutter test app urls to the 0.0.33 release.

Author: Dor-bl

.github/workflows/functional-test.yml

@@ -245,8 +245,8 @@ jobs:
       XCODE_VERSION: 16.4
       IOS_VERSION: 18.5
       IPHONE_MODEL: iPhone 16
-      FLUTTER_ANDROID_APP: "https://github.com/AppiumTestDistribution/appium-flutter-server/releases/latest/download/app-debug.apk"
-      FLUTTER_IOS_APP: "https://github.com/AppiumTestDistribution/appium-flutter-server/releases/latest/download/ios.zip"
+      FLUTTER_ANDROID_APP: "https://github.com/AppiumTestDistribution/appium-flutter-server/releases/download/0.0.33/app-debug.apk"
+      FLUTTER_IOS_APP: "https://github.com/AppiumTestDistribution/appium-flutter-server/releases/download/0.0.33/ios.zip"
       PREBUILT_WDA_PATH: ${{ github.workspace }}/wda/WebDriverAgentRunner-Runner.app
 
     steps: