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/application/ports/calendar_ports.rs

@@ -3,11 +3,9 @@ use crate::application::dtos::calendar_dto::{
     UpdateCalendarDto, UpdateEventDto,
 };
 use crate::common::errors::DomainError;
-use async_trait::async_trait;
 use chrono::{DateTime, Utc};
 
 /// Port for external calendar storage mechanisms
-#[async_trait]
 pub trait CalendarStoragePort: Send + Sync + 'static {
     // Calendar operations
     async fn create_calendar(
@@ -111,7 +109,6 @@ pub trait CalendarStoragePort: Send + Sync + 'static {
 /// All methods require an explicit `user_id` parameter for authorization.
 /// The CalDAV protocol handler extracts the user identity from JWT claims
 /// and passes it through.
-#[async_trait]
 pub trait CalendarUseCase: Send + Sync + 'static {
     // Calendar operations
     async fn create_calendar(