Migrate 5 java classes to kotlin

[YasinMoridi]

Description

This PR migrates 5 Java classes in the org.thoughtcrime.securesms package to Kotlin as part of ongoing code modernization efforts.

Files converted:

• BlockUnblockDialog.java → BlockUnblockDialog.kt (converted to object with @JvmStatic for Java compatibility)
• KbsEnclave.java → KbsEnclave.kt (converted to data class)
• Unbindable.java → Unbindable.kt (converted to interface)
• MasterSecretListener.java → MasterSecretListener.kt (converted to interface)
• TextSecureExpiredException.java → TextSecureExpiredException.kt (converted to Exception class)

Changes made:

• Used Kotlin idioms (when expressions, properties, null safety)
• Removed original Java files to prevent Redeclaration errors
• Maintained full compatibility with existing Java code via @JvmStatic annotations where needed

Testing:

• Built the project successfully with ./gradlew build
• No functional changes were introduced — this is a pure language migration
• [Add any specific manual testing you did here]

No new features or behavior changes are introduced in this PR.