Implements 44 tests covering all functions and edge cases:
- parse_version: handles valid versions, suffixes, and invalid inputs
- _check_operator: tests all comparison operators (>=, <=, >, <, ==, !=)
- satisfies: validates single/multiple specifiers and complex combinations
- get_supported_versions: covers success cases and error conditions
- version_matrix_command: tests defaults, custom options, and error handling

Coverage: 78 statements, 0 missed (100%)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Removes the module from sys.modules before using runpy.run_module() to avoid
the warning: "module found in sys.modules after import of package but prior
to execution; this may result in unpredictable behaviour"

The fix ensures clean module execution by temporarily removing the module from
sys.modules and restoring it afterwards, eliminating the warning while
maintaining test coverage.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Renamed test_version_matrix.py to test_version_matrix_command.py to avoid
naming conflict with .rhiza/tests/utils/test_version_matrix.py which tests
the original utility script.

This resolves the pytest error:
"imported module 'test_version_matrix' has this __file__ attribute which is
not the same as the test file we want to collect"

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Adds two test cases to test_cli_commands.py that cover the CLI wrapper
function for version-matrix, testing both default and custom candidate
parsing. This brings test coverage from 99% to 100%.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>