ci: Fix CI test failures

Add missing test dependencies to requirements-test.txt:

  - pytest-cov>=4.0.0 (for coverage reporting)

  - pytest-mock>=3.10.0 (for mock fixtures)

Add missing __init__.py to tests/core/ package

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

Author: toraidl

requirements-test.txt

@@ -1,3 +1,5 @@
-pytest
-coverage
+pytest>=7.0.0
+pytest-cov>=4.0.0
+pytest-mock>=3.10.0
+coverage>=7.0.0
 mock