perf: replace dyn trait objects with concrete types to eliminate vtable overhead

Remove async-trait dependency and use native Rust async fn in traits.
Replace Arc<dyn Trait> with Arc<ConcreteType> throughout the codebase
to enable monomorphization and eliminate dynamic dispatch overhead.

Key changes:
- Remove write-behind cache (no implementation existed)
- Fix should_transcode static method call
- Use ContactStorageAdapter directly instead of dyn AddressBookUseCase
- Clean up unused trait imports across services and DI

https://claude.ai/code/session_01EbAFEfyJNLRmJHmmYDX3Tt

src/domain/repositories/calendar_event_repository.rs

@@ -1,13 +1,11 @@
 use crate::common::errors::DomainError;
 use crate::domain::entities::calendar_event::CalendarEvent;
-use async_trait::async_trait;
 use chrono::{DateTime, Utc};
 use uuid::Uuid;
 
 pub type CalendarEventRepositoryResult<T> = Result<T, DomainError>;
 
 /// Repository interface for CalendarEvent entity operations
-#[async_trait]
 pub trait CalendarEventRepository: Send + Sync + 'static {
     /// Creates a new calendar event
     async fn create_event(