Unit tests for each core module

[ulises-jeremias]

Summary

pytest suite covering core modules with fixtures.

CNA mapping

CNA: packages/create-node-app-core/tests/*.test.mts.

Acceptance criteria

• Tests for errors, paths, git/cache (mocked), loaders, config, installer
• Coverage contributes to workspace threshold

Blocked by

none

Blocks

none

Reference

Parity matrix (workspace): knowledge/create-python-app-parity-matrix.md
Reference repo: https://github.com/Create-Node-App/create-node-app

Parent epic

#4