Fix cstest_py and add negative tests.

[Rot127]

Your checklist for this pull request

• I've documented or updated the documentation of every API function and struct this PR changes.
• I've added tests that prove my fix is effective or that my feature works (if possible)

Detailed description

Fixes a bug in cstest_py which didn't report failing tests.
The C cstest was luckily not affected.

It also fixes several small leaks which occur when tests fail.

Test plan

Because of this the PR adds negative tests so it won't happen again.

Closing issues

...

[Copilot]

Pull Request Overview

This PR fixes a bug in cstest_py that prevented failing tests from being properly reported and adds negative test cases to prevent regression. It also addresses memory leaks that occurred when tests failed.

Key changes:

• Fixed cstest_py to return test failures correctly by replacing non-returning _check() function calls with direct conditional checks
• Added memory cleanup functions to fix leaks in the C cstest implementation
• Created six negative test cases to verify that test failures are properly detected

Reviewed Changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
bindings/python/cstest_py/src/cstest_py/cstest.py	Fixed bug where comparison failures didn't return and added exit on inconsistent statistics
suite/cstest/src/test_case.c	Added cs_free() call in failure macro to prevent memory leaks
suite/cstest/src/cstest.c	Added cleanup_test_files() function and calls to free memory on exit paths
suite/cstest/CMakeLists.txt	Added six negative test cases marked with WILL_FAIL property
suite/run_tests.py	Added logic to run negative tests and verify they fail as expected
tests/negative/should_fail_*.yaml	Six new test case files designed to fail for different reasons
.github/workflows/CITest.yml	Updated CI to run negative tests and use more specific valgrind test paths

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