Retain AchievementManager UI notifier instead of weakly referencing it

[Copilot]

The reviewed code stored AchievementManager's UiNotifier in a WeakReference, which allowed notifier callbacks to disappear unexpectedly. This change keeps the notifier alive until it is explicitly cleared, matching the intended callback lifecycle.

• Notifier lifetime

  • Replace WeakReference<UiNotifier?> with a strong UiNotifier?
  • Update setUiNotifier() to store the notifier directly and clear it on null

• Android adapter path

  • Update setCurrentActivity() to install the toast-backed notifier as a strong reference
  • Clear the notifier when the activity is cleared, preserving explicit lifecycle control

• Regression coverage

  • Add a focused test that verifies:
    • the exact notifier instance is retained after setUiNotifier(notifier)
    • the notifier is removed after setUiNotifier(null)

private var uiNotifier: UiNotifier? = null

fun setUiNotifier(notifier: UiNotifier?) {
    this.uiNotifier = notifier
}

[Copilot]

Pull request overview

This PR fixes an unintended notifier lifecycle issue in AchievementManager where UI callbacks could disappear due to storing the UiNotifier in a WeakReference. It updates the manager to retain the notifier strongly until it is explicitly cleared, which better matches the expected callback lifecycle (including the Android toast-backed notifier path).

Changes:

• Replace WeakReference<UiNotifier?> storage with a strong UiNotifier? field.
• Update setCurrentActivity() to install/clear the toast-backed notifier via strong assignment (sets null when activity is cleared).
• Add an Android instrumentation regression test verifying the notifier instance is retained and then cleared.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
app/src/main/java/roboyard/logic/achievements/AchievementManager.kt	Switch notifier storage to a strong reference; adjust Android activity adapter setup and update-nudge dispatch accordingly.
app/src/androidTest/java/roboyard/eclabs/achievements/AchievementManagerTest.java	Add regression test asserting setUiNotifier() retains the exact instance and clears it when set to null.