Add pytests for the Lua-Python interface

[cclauss]

As requested in:

• GitHub Actions: Complete tests #94

% pytest tests/test_lua_via_pytest.py

============================= test session starts ==============================
platform linux -- Python 3.14.6, pytest-9.1.0, pluggy-1.6.0
rootdir: /home/runner/work/lunatic-python/lunatic-python
collected 7 items

tests/test_lua_via_pytest.py ...ssss                                     [100%]

========================= 3 passed, 4 skipped in 0.02s =========================

# TODO: Remove this skip marker and fix the segmentation fault issues.
skip_segfault = pytest.mark.skip(
    reason="Segmentation fault in LuaJIT when accessing table elements"
)

[leso-kn]

As requested in:

Not exactly :) I assume you are referring to #94 (comment), where I asked whether we can call the existing tests inside the tests/ folder.

This PR rewrites a small amount of tests for pytest.

Please note that lunatic-python already uses the doctest library.

I will close this issue as invoking python tests/test_lua.py should be sufficient to implement the Github Actions pipeline.