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/dedup_service.rs

@@ -31,7 +31,6 @@
 //! - 30-50% storage reduction typical
 //! - Faster uploads for existing content (instant dedup)
 
-use async_trait::async_trait;
 use bytes::Bytes;
 use futures::stream::{self, StreamExt};
 use futures::{Stream, TryStreamExt};
@@ -802,7 +801,6 @@ impl DedupService {
 
 // ─── Port implementation ─────────────────────────────────────────────────────
 
-#[async_trait]
 impl DedupPort for DedupService {
     async fn store_bytes(
         &self,