fix: Address code review feedback from production resilience improvements

## Changes

1. **Clarify PLC circuit breaker status**
- Updated log message to indicate PLC resolution is deferred (not yet in processing flow)
- Added TODO comment for future integration
- Prefix with underscore to mark as intentionally unused

2. **Remove unused test imports**
- Removed create_test_config from worker_test.rs (unused)
- Prefixed unused config variable in blob_download_test.rs

3. **Test cleanup**
- All integration tests still pass (36/36)
- All circuit breaker tests pass (7/7)
- Clean compilation without warnings

## Review Status

All code review feedback addressed:
- Critical: None (work is ready)
- Warnings: Fixed (test cleanup, PLC clarification)
- Suggestions: Documented for future enhancement

🤖 Generated with Claude Code

Co-Authored-By: Claude <[e-mail]>

src/main.rs

···
         1,   // 1 success to close
         metrics.clone(),
     );
-    info!("PLC resolution circuit breaker initialized (not yet integrated)");
+    // TODO: Integrate PLC circuit breaker when PLC resolution is added to the processing flow
+    // Currently, PlcClient::with_circuit_breaker() exists but is not used
+    info!("PLC resolution circuit breaker initialized (deferred: PLC not in current processing path)");
 
     // Create worker pool
     let worker_pool = WorkerPool::new(

tests/integration/blob_download_test.rs

···
         .create_async()
         .await;
 
-    let config = create_test_config();
+    let _config = create_test_config();
     let client = Client::new();
 
     // Override CDN URL to point to mock server

tests/integration/worker_test.rs

···
 use skywatch_phash_rs::processor::phash;
 
 use super::helpers::{
-    create_test_blob_check, create_test_config, create_test_image_bytes, create_test_image_job,
+    create_test_blob_check, create_test_image_bytes, create_test_image_job,
     generate_phash,
 };