Add dll binary path for cadet core pypi distribution

[hannahlanzrath]

Fixes and add tests for #77

When this PR is merged we should to a bug fix release!

Summary

Make CADET-Python correctly find the CADET-Core DLL when installed via the cadet-core PyPI package (not just conda), and add CI coverage for that install path.

1. cadet/cadet.py : resolve_cadet_paths now falls back to the cadet_core package's own directory (Path(cadet_core.__file__).parent) to locate the shared library whenever it isn't found under the originally-resolved root. This handles two PyPI problems: binaries nested inside site-packages/cadet_core/ rather than at the venv root, and (discovered via CI) cadet-cli/createLWE console scripts sometimes living in a completely different prefix than the cadet_core package itself (seen on macOS GH Actions runners). Also added the SONAME-versioned libcadet.0.dylib as a fallback filename on macOS.

2. tests/test_cadet.py : new test_create_lwe_and_run_cli_smoke, parametrized over the conda-autodetected install and the cadet-core PyPI install (skipped via pytest.importorskip if cadet_core isn't present). Runs create_lwe() + run_simulation() and checks for a clean return code.

3. .github/workflows/pipeline.yml : new test-pypi-job: a plain-Python (no conda) matrix job that pip installs CADET-Python + cadet-core and runs the test suite, exercising the PyPI install path end-to-end across Linux/Windows/macOS.

4. tests/test_install_path_settings.py : relaxed test_autodetection to check that cadet_dll_path/cadet_cli_path exist rather than asserting they share a parent directory with the install root, since that invariant doesn't hold for PyPI installs where the dll and the console scripts can live under different prefixes.

[jbreue16]

Fix works for me,

from cadet import Cadet

c = Cadet()

print("DLL:", c.cadet_dll_path)
print("CLI:", c.cadet_cli_path)

prints None for the DLL on master, but gives a correct path with this branch