Testing - Robust test coverage

[bordumb]

Description:

This PR introduces a foundational test suite and significantly refactors the GitHub Actions workflow to improve reliability and efficiency.

Changes:

• Added Foundational Tests:
  • Unit tests for core ECS components (SimulationState).
  • Contract tests for the SystemManager.
  • An integration smoke test to validate the end-to-end simulation loop.
• Integrated Code Coverage:
  • The test job now reports on code coverage for agent-core and agent-engine.
  • The build will fail if coverage drops below an 80% threshold, ensuring a consistent quality standard.
• Refactored CI Workflow:
  • Consolidated the CI pipeline into a single, parallelized job using a matrix strategy.
  • This change reduces code duplication and speeds up the feedback loop by running linting, type-checking, and testing concurrently.