Add unit tests for services

**Description**
Currently core lacks proper serialization support.

**Proposed solution**
Add configurable serialization with sensible defaults.

**Priority**: Low/Medium

The issue names no files, entry points, or existing tests. Start by locating the core services and current serialization-related code, then inspect how services are tested. Done means configurable serialization has sensible defaults and unit tests cover the supported behavior.

Written by the indexing model from the issue text.