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/services/password_hasher.rs

@@ -12,7 +12,6 @@
 
 use argon2::password_hash::SaltString;
 use argon2::{Algorithm, Argon2, Params, PasswordHash, PasswordHasher, PasswordVerifier, Version};
-use async_trait::async_trait;
 use rand_core::OsRng;
 
 use crate::application::ports::auth_ports::PasswordHasherPort;
@@ -57,7 +56,6 @@ impl Argon2PasswordHasher {
     }
 }
 
-#[async_trait]
 impl PasswordHasherPort for Argon2PasswordHasher {
     async fn hash_password(&self, password: &str) -> Result<String, DomainError> {
         let pwd = password.to_owned();