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/infrastructure/repositories/pg/session_pg_repository.rs

@@ -1,4 +1,3 @@
-use async_trait::async_trait;
 use chrono::Utc;
 use futures::future::BoxFuture;
 use sqlx::{PgPool, Row};
@@ -39,7 +38,6 @@ impl SessionPgRepository {
     }
 }
 
-#[async_trait]
 impl SessionRepository for SessionPgRepository {
     /// Creates a new session using a transaction
     async fn create_session(&self, session: Session) -> SessionRepositoryResult<Session> {
@@ -291,7 +289,6 @@ impl SessionRepository for SessionPgRepository {
 }
 
 // Implementation of the storage port for the application layer
-#[async_trait]
 impl SessionStoragePort for SessionPgRepository {
     async fn create_session(&self, session: Session) -> Result<Session, DomainError> {
         SessionRepository::create_session(self, session)