Migrate var usage in data classes

[Copilot]

Summary

• Migrated mutable data-class properties to immutable patterns where safe:
  • ProxyState.now, Profile.download, TunDevice.stack, and NetworkInfo fields are now immutable.
• Updated mutation call sites to use immutable updates:
  • ProxyActivity now replaces list entries via copy(...).
  • NetworkObserveModule now updates map entries via computeIfPresent(..., copy(...)).
• For ConfigurationOverride and nested models that rely on mutable property references in settings UIs, removed the data modifier to preserve existing behavior while eliminating var usage in data class declarations.

Validation

• ./gradlew --no-daemon spotlessCheck test assemble (before and after changes): fails in this environment due inability to resolve Android Gradle plugin com.android.application:9.1.1 from configured repositories (network/repository access issue).
• parallel_validation:
  • Code Review: completed; one naming-style suggestion remains (subjective conflict).
  • CodeQL Security Scan: no analyzable language changes detected.