Add changelog for version 1.6.0 with highlights on icons, null safety, and code improvements

Author: egdels

fastlane/metadata/android/en-US/changelogs/10600.txt

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+1.6.0
+• Adaptive launcher icons for all devices and launchers.
+• Improved null safety across the entire codebase.
+• New SharesDiffCallback for smoother list updates.
+• Stricter code quality checks.
+• Updated WorkManager to 2.11.1.
+• Removed unused resources and simplified dialogs.
+• New unit tests for caching, utilities & more.