Optimize pattern handling and memory management

[mmiheev]

Changes

Added Back Button to PreferencesActivity

• Added back button navigation to PreferencesActivity toolbar following existing pattern from other activities
• Extracted intent extras handling to separate method for better code organization
• Used AppCompat resources for back icon compatibility

Refactored SecPreferenceFragment

• Added dedicated methods for pattern result handling:
  • handleCreatePatternResult()
  • handleEnterPatternResult()
  • savePattern()
  • enablePatternFeatures()
  • resetPatternSelection()

Memory Management

• Explicit nullification of globalContext, enableAdminPref, and enableDeviceCheckPref in onDestroy()
• Added isAdded() checks in onActivityResult() to prevent NPE

Lifecycle Safety

• Implemented fragment state validation before UI operations
• Protected against operations when fragment is detached

Technical Details

• Maintained full backward compatibility
• No changes to public API or user-facing behavior
• Reduced method complexity by extracting helper functions
• Improved error resilience during configuration changes

[mmiheev]

Back button functionality has been added to PreferencesActivity.