refactor: 🛠️ improve logging architecture and cleanup

- **✨ Features**
  - Rename structured logger output channel to "LiteLLM Structured" to prevent collision with legacy logs.
- **🧹 Chores**
  - Remove unused `setLogLevel` command and registration logic.
  - Bump project version to `1.5.0-dev2` and apply minor formatting to `package.json`.
- **🧪 Tests**
  - Add unit test verifying that the structured logger initializes with the correct, distinct output channel name.