feat: Migrate PreferencesManager to DataStore with Encrypted Storage

[PavloNetrebchuk]

Migrates PreferencesManager from SharedPreferences to Jetpack DataStore Preferences with AES-256-GCM encryption for sensitive data using Android Keystore.

DataStore Migration:

• Replaced SharedPreferences with DataStore
• Introduced type-safe preference keys using stringPreferencesKey, longPreferencesKey, booleanPreferencesKey
• Updated clearCorePreferences() and clearCalendarPreferences() to suspend functions
• Added androidx.datastore:datastore-preferences:1.2.0 dependency

Encryption Implementation:

• Created DataStoreEncryption class using Android Keystore + AES-256-GCM
• Encrypted sensitive fields:
  • accessToken
  • refreshToken
  • pushToken
  • user (JSON)
  • profile (JSON)

Security Details:

• Algorithm : AES-256-GCM
• Key Storage : Android Keystore (hardware-backed when available)
• IV Length : 2 bytes (random per encryption)
• Auth Tag : 128 bits
• Format : Base64(IV + ciphertext + auth_tag)

Motivation

SharedPreferences limitations:

• No encryption for sensitive data
• Synchronous API blocks the calling thread
• No type safety for keys

New implementation advantages:

• Sensitive tokens encrypted at rest
• Keys stored in Android Keystore (never exportable)
• Type-safe key definitions
• Guaranteed atomic writes

[openedx-webhooks]

Thanks for the pull request, @PavloNetrebchuk!

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