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/trash_repository.rs

@@ -1,10 +1,8 @@
-use async_trait::async_trait;
 use uuid::Uuid;
 
 use crate::common::errors::Result;
 use crate::domain::entities::trashed_item::TrashedItem;
 
-#[async_trait]
 pub trait TrashRepository: Send + Sync {
     async fn add_to_trash(&self, item: &TrashedItem) -> Result<()>;
     async fn get_trash_items(&self, user_id: &Uuid) -> Result<Vec<TrashedItem>>;