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/thumbnail_service.rs

@@ -1,4 +1,3 @@
-use async_trait::async_trait;
 use bytes::Bytes;
 use image::{ImageFormat, imageops::FilterType};
 /**
@@ -458,7 +457,6 @@ impl From<PortThumbnailSize> for ThumbnailSize {
     }
 }
 
-#[async_trait]
 impl ThumbnailPort for ThumbnailService {
     fn is_supported_image(&self, mime_type: &str) -> bool {
         ThumbnailService::is_supported_image(mime_type)